Fixed vs Flexible Energy Contracts: The Complete Guide for UK Finance Directors

01 — The stakes
Why this decision matters

For most UK businesses, energy is one of the largest controllable operating costs – often second only to payroll. Yet the decision about how to buy that energy is made surprisingly often on autopilot. The contract rolls. The renewal lands on someone’s desk. A quote is accepted. The cycle repeats.

That habit costs money. Not because anyone is being negligent, but because energy procurement is genuinely complicated – and the difference between a well-timed fixed contract and a poorly-timed one can be 20% or more on your annual bill. For an organisation spending £500,000 a year on energy, that is a £100,000 swing. For larger estates, the numbers get bigger fast.

This guide is written for finance directors, procurement managers, and operations leads who have been asked to make this call – and want to understand the choice properly before signing anything.

02 — Option one
Fixed price contracts explained

A fixed price energy contract locks in a single unit rate (pence per kWh) for the duration of the contract – usually one, two, or three years. Whatever happens in the wholesale energy market over that period, your unit rate does not move.

The appeal is obvious. You know exactly what you’ll pay. Budgeting becomes straightforward. Forecasting is clean. There are no surprises in the finance pack when wholesale prices spike.

The trade-off is just as obvious. If wholesale prices fall during the term, you carry on paying the higher fixed rate. The supplier, who has already locked in their own hedge against your contract, keeps the difference. That is the deal you signed.

When fixed makes sense

• Budget certainty matters more than absolute price. If your board demands predictable energy spend – or your business model can’t absorb price volatility – fixed is the right answer.
• You’re entering a long-term capital commitment. If you’re building a 10-year financial model on a new site, fixed protects the underlying assumptions.
• Markets are at or near cycle lows. Locking in a low fixed rate during a market trough is the textbook play – if you can identify the trough, which is harder than it sounds.
• You don’t have time or resource to manage a flexible contract. Flexible buying requires active engagement. Fixed lets you sign once and forget.

When fixed becomes a problem

The risk with fixed is concentrated entirely at the moment you sign. If you fix at a market peak – which has happened repeatedly to UK businesses over the last five years – you are locked into above-market pricing for the entire term. By the time the contract ends, you have potentially paid hundreds of thousands more than you needed to.

This is exactly why timing matters more than the contract structure itself. A well-timed flexible contract usually beats a badly-timed fixed contract. A well-timed fixed contract often beats a poorly-managed flexible one. The structure is not the strategy – the timing is.

03 — Option two
Flexible contracts explained

A flexible energy contract takes a different approach. Instead of locking in one rate for the whole term, you buy your energy in tranches across the contract period – sometimes month-by-month, sometimes quarter-by-quarter, sometimes against a rolling forward curve.

The mechanics vary, but the principle is the same: you take a position on part of your volume now, leave the rest open, and continue buying as market conditions evolve. Done well, this lets you take advantage of market dips and avoid locking in at peaks.

The structures you’ll encounter

Flexible contracts come in a few common shapes:

• Click-and-fix: You agree the volume upfront and then place “click” orders to fix portions of it at the wholesale rate of the day, until the full contract volume is locked in.
• Tranche buying: Volume is split into pre-agreed tranches (e.g. 20% per quarter) and bought at the prevailing market price each tranche window.
• Pass-through with hedging: You pay the wholesale rate plus a managed fee, with optional hedging against an index. More transparency, more variability.
• Basket arrangements: Multi-site portfolios pooled into a single flexible position, often used by larger organisations to share procurement infrastructure.

When flexible makes sense

• Your business can absorb some price variability. If a 10-15% swing in monthly energy spend wouldn’t break your forecast, flexible gives you upside.
• You have access to market intelligence. Flexible only works well if someone is actually watching the market and making informed buying calls.
• Your consumption is large and predictable. Bigger volumes attract better flexible terms. Predictable usage profiles let suppliers offer sharper pricing.
• You operate across multiple sites. Flexibility lets you align procurement with your actual operational rhythm rather than every site’s individual contract end-date.

What flexible asks of you

Flexible contracts demand engagement. Either yours – someone in the business has to read market reports, take buying calls, and document why decisions were made – or your broker’s, which means you need a broker who actually does that work and isn’t just collecting commission on autopilot.

The risk is the same as fixed but in the opposite direction. If you take flexible and the market spikes hard before you’ve fixed your tranches, you can end up paying significantly more than a fixed contract would have cost.

04 — Option three
A third option: SMARTFLEX

The fixed-versus-flexible binary is genuinely useful as a framing – but it’s not the whole picture. Most large UK organisations now use some form of structured flexible arrangement that blends the two.

At eyebright we call this SMARTFLEX – a risk-managed approach that combines flexibility with structured controls. The mechanics vary by client but the core idea is the same: you don’t sit fully exposed to market volatility, but you’re not stuck on a single fixed rate either.

How SMARTFLEX works in practice

SMARTFLEX contracts typically include some or all of the following:

• Tranche buying with pre-agreed risk limits – you commit to taking positions, but with caps on how much exposure you’ll carry at any one time
• Stop-loss triggers that automatically close positions if wholesale rates breach an agreed level
• Profile-aware purchasing that aligns your buying with your actual usage curve – so seasonal businesses don’t carry winter-rate exposure on summer volumes
• Scheduled review points where the strategy can be revisited as conditions change, rather than locked in for years

The advantage is that you get most of the upside of flexibility – the ability to take advantage of market falls, the option not to lock in at peaks – without carrying the full downside risk that pure flexible exposure entails.

The trade-off is complexity. SMARTFLEX is harder to operate than either fixed or flexible. It needs an active broker or in-house team that genuinely understands hedging mechanics. The structure is only as good as the people running it.

05 — Decision framework
Which fits your business?

The honest answer: it depends. But the variables that determine the right answer are knowable. Here is the framework we use with our clients.

06 — The hardest part
The timing question

Whichever structure you choose, the timing of your decision matters more than the structure itself. This is the part nobody outside the energy market discusses honestly enough.

Wholesale energy prices in the UK have moved by 60% or more within twelve-month windows multiple times in the last five years. The same fixed price contract, signed three months earlier or three months later, can cost a business hundreds of thousands of pounds more or less – for the exact same energy.

This is not an argument against fixed contracts. It is an argument for making the buying decision with information rather than by default. If your contract end date is approaching, the question is not whether to fix or go flexible. The question is: where is the market today relative to the cycle, and what does that suggest about the right strategy for the next 12-36 months?

Flexible contracts offer real advantages and like any tool, they work best when paired with a clear plan for what comes next.

Answering that requires market intelligence – which is exactly why most large organisations use a broker or in-house team that monitors the market every day. Daily market data is not a nice-to-have for businesses with serious energy spend. It is the difference between buying with information and buying blind.

07 — What to avoid
Common mistakes

The mistakes we see most often in UK procurement decisions:

1. Fixing at the peak. Boards demand certainty when prices are high – exactly the wrong moment. Lock in cycle highs and you carry that pain for the full term.
2. Going flexible without active management. Flexible contracts that sit untouched are not flexible – they’re random. Without someone watching the market, you’ve just signed up for whatever pricing happens to land.
3. Treating renewal as admin. Energy procurement is a multi-hundred-thousand-pound decision. It deserves proper market analysis, not a comparison of three quotes from a preferred broker panel.
4. Ignoring contract end-date alignment across an estate. Multi-site organisations that let every site renew on its own cycle never get the buying power their portfolio could deliver. Aligning contract end dates is one of the highest-leverage moves available.
5. Not understanding what “flexible” actually means in your contract. Some “flexible” contracts are barely more flexible than fixed. Read the structure properly, or have someone read it for you.

08 — The bottom line
What to do with all this

If you take three things from this guide, take these:

One. The fixed vs flexible choice is real and matters – but timing matters more than structure. A well-timed fixed contract usually beats a badly-timed flexible one and vice versa.

Two. The right answer depends on your spend level, your tolerance for budget variability, and whether you have access to ongoing market intelligence. There is no single correct choice.

Three. Whatever you choose, the worst version of the decision is the autopilot version. Make the call with information, with timing in mind, and ideally with someone independent helping you read the market. The cost of getting this wrong is usually far higher than the cost of taking the time to get it right.