Pay-Per-Mile Tax and PHEVs: Why the Government Wants to Track Your Car

Imagine paying road tax based entirely on how far you drive — fair in principle, until you realise that the car sitting next to you at the traffic lights might be running purely on petrol while yours has barely touched its battery. That's the exact problem facing Treasury officials as they try to make the UK's forthcoming pay-per-mile vehicle excise duty system work for plug-in hybrid drivers.

What's Actually Being Proposed

According to reporting by AutoExpress, there are serious discussions underway about tracking plug-in hybrid electric vehicles (PHEVs) to ensure they're taxed appropriately under the planned pay-per-mile electric Vehicle Excise Duty (eVED) system, due to launch in April 2028.

The core proposal is this: because PHEVs can run on either electricity or petrol depending on how they're driven, a blanket flat-rate or simple mileage-based charge wouldn't accurately reflect their real-world emissions or fuel consumption. A driver who plugs in religiously and does most of their miles on electric power is a fundamentally different proposition from someone who never charges and uses their PHEV as a glorified petrol car with a heavier kerb weight.

The solution being floated involves tracking the proportion of miles driven in electric mode versus combustion mode — essentially requiring PHEVs to report split mileage data. This would allow HMRC or the relevant authority to apply differentiated rates depending on how "electric" a driver's usage actually is.

It's an ambitious idea. And it raises a stack of questions that go well beyond the headline.

Why This Matters: The PHEV Problem in Plain English

To understand why this is complicated, you need to appreciate what PHEVs actually are in practice. On paper, they're the best of both worlds — a battery for short urban trips, a petrol engine for longer journeys. In reality, studies have repeatedly shown that many PHEV drivers — particularly company car drivers — rarely charge their vehicles at all.

A 2020 study by Transport & Environment found that real-world PHEV emissions were, on average, two to four times higher than official figures suggested. The official test cycles assumed regular charging. Real drivers often don't bother.

This matters enormously for a pay-per-mile system. If the government simply charges PHEVs the same rate as pure EVs because they're technically capable of zero-emission driving, it would be wildly unfair to other road users and would undermine the environmental logic of the entire scheme. But if it charges them the same as petrol cars, it penalises drivers who genuinely do use their vehicles responsibly.

Hence the tracking proposal. It's not just a revenue-raising exercise — it's an attempt to make the system intellectually coherent.

The Legal Angle: Data, Privacy, and Precedent

This is where things get genuinely thorny. Tracking vehicle location or usage data on a national scale raises significant legal questions under UK data protection law — specifically the UK General Data Protection Regulation (UK GDPR) and the Data Protection Act 2018.

Any scheme that involves continuous or near-continuous monitoring of a vehicle's movement would need to satisfy several legal tests. The data collected would need to be:

• Necessary and proportionate to the stated purpose
• Processed lawfully, with a clear legal basis (most likely a statutory obligation)
• Retained only as long as necessary
• Secure against misuse or unauthorised access

The government has previous form here. The Road Vehicles (Construction and Use) Regulations 1986 already require vehicles to meet certain technical standards, and successive governments have used legislation to mandate data reporting from vehicles — think MOT history, emissions testing, and the DVLA's existing access to manufacturer data for type approval.

But a live or near-live tracking requirement would be a significant escalation. Privacy campaigners are likely to challenge any scheme that creates what amounts to a national database of where every PHEV driver goes and when.

There's also the question of who holds the data. If it's stored by manufacturers and reported periodically (say, annually at MOT), that's one thing. If it requires a government-linked black box in every PHEV, that's quite another — and would likely require primary legislation, not just a statutory instrument.

The Infrastructure Act 2015 and subsequent road pricing consultations have touched on these issues, but no comprehensive legal framework for mass vehicle tracking currently exists in the UK. Parliament would need to act, and the political sensitivities are considerable.

What Drivers Should Know Right Now

If you own or are considering buying a PHEV, here's what the current proposals mean in practical terms:

1. Nothing changes before April 2028 at the earliest The eVED system isn't live yet. PHEVs currently pay standard Vehicle Excise Duty based on CO₂ emissions and list price. From April 2025, EVs began paying VED for the first time, but PHEVs have been subject to VED throughout. The pay-per-mile element is still in development.

2. Your OBD port and telematics may become relevant Modern PHEVs already record split mileage data — how many miles were driven in EV mode versus hybrid mode — accessible via the on-board diagnostics (OBD) port. Some manufacturers store this in cloud systems. If the government requires this data for tax purposes, it may not require new hardware at all, just a legal obligation to report what's already being recorded.

3. Company car drivers face particular scrutiny The Benefit-in-Kind (BIK) tax system already applies different rates to PHEVs based on electric range. HMRC has form in challenging PHEV claims where drivers cannot demonstrate actual electric usage. A pay-per-mile system would extend this logic to personal taxation, not just employer reporting.

4. Keep records of your charging habits If you're a conscientious PHEV driver who charges regularly, it's worth keeping evidence — home charging records, public charging receipts, smart charger app data. If a dispute arises about your electric-to-petrol ratio, this could be invaluable.

5. Consider how this affects your next purchase decision If you're planning to buy a PHEV in the next two to three years, factor in the likelihood of a usage-based tax element from 2028. A vehicle with a longer electric range — and one you'll actually charge — is likely to attract lower charges under any sensible scheme.

The Broader Context: Road Pricing in the UK

The pay-per-mile debate doesn't exist in isolation. The UK government has been wrestling with a fundamental fiscal problem: as more drivers switch to EVs, fuel duty revenues — which currently raise around £25 billion a year — will collapse. Fuel duty and VED together form a critical plank of public finances, and without a replacement mechanism, the Treasury faces a significant structural shortfall.

The Office for Budget Responsibility has flagged this repeatedly. The Transport Select Committee has called for action. And the government's own net zero commitments make the transition away from petrol and diesel inevitable.

Pay-per-mile is the most logical replacement — you pay for road use based on actual use, rather than through a proxy like fuel consumption. In principle, it's fairer. A driver who does 5,000 miles a year pays less than one who does 20,000, regardless of what they drive.

But PHEVs sit awkwardly in this framework. They're a transitional technology — more efficient than pure petrol, less straightforward than pure EVs. Getting their taxation right is genuinely difficult, and the tracking proposal reflects that difficulty honestly.

Looking Ahead: What Comes Next

The April 2028 target is real but tight. For a PHEV tracking system to be operational by then, the government would need to:

• Consult publicly on the data collection methodology
• Pass enabling legislation (or use existing powers creatively)
• Agree a framework with vehicle manufacturers for data sharing
• Build or commission the IT infrastructure to process millions of vehicles' worth of mileage data
• Communicate clearly with drivers about what's required of them

That's a formidable to-do list for a government that has struggled to deliver major IT projects on time and on budget. There's a reasonable chance that PHEVs end up on a flat-rate eVED charge initially, with usage-based refinement phased in later.

What's clear is that the era of PHEVs being a tax-efficient loophole is drawing to a close. The government has noticed that many PHEV drivers aren't driving as cleanly as the incentive structure assumed, and it intends to correct that — one way or another.

For drivers, the message is straightforward: if you own a PHEV, use it as intended. Charge it regularly, drive on electric power where you can, and keep records. The tax system is moving towards rewarding exactly that behaviour — and penalising those who don't.

Source: AutoExpress — ["Plan to track plug-in hybrid cars to make pay-per-mile tax fairer"](https://www.autoexpress.co.uk/news/369628/plan-track-plug-hybrid-cars-make-pay-mile-tax-fairer)