The Detour Tax: What Unreliable Public Charging Adds to a UK EV Bill in 2026

The cost that never appears on the tariff board

A public charging tariff is a simple promise: so many pence per kilowatt-hour, subject to connection fees and parking terms. What it does not capture is the session that never starts, the connector that will not release, the app that times out at the payment stage, or the charger that delivers a fraction of its advertised speed. For UK drivers in 2026, those failures are not merely irritating. They carry a measurable cost that sits outside the published rate and quietly inflates the real price of public charging.

This is the reliability discount in reverse. A network that works when needed can justify a higher headline tariff; a network that fails imposes a surcharge on every driver who relies on it. The task is to count that surcharge properly.

The anatomy of a failed public charge

Failures are rarely a single event. A driver arrives at a site, discovers a unit is offline, moves to another bay, finds a connector fault, restarts the session, calls support, and eventually leaves with less charge than planned. Each step adds cost.

The direct costs are straightforward: additional miles driven to reach a working charger, a second connection fee, a pre-authorisation hold that temporarily reduces available funds, and sometimes a parking charge incurred while trying to resolve the problem. The indirect costs are larger but less visible: time spent waiting, the value of arriving late, and the contingency top-up bought at a premium elsewhere because the planned cheap charge did not materialise.

There is also a planning cost. Drivers who have been let down learn to build buffers into journeys, to arrive with more charge than strictly necessary, and to favour familiar networks over cheaper ones. That behaviour is rational, but it has a price. It means paying for insurance against unreliability, often at the most expensive points on the route.

Detour arithmetic for a typical UK driver

Consider an illustrative driver covering 12,000 miles a year in an electric car averaging 3.8 miles per kWh. Around 30 per cent of that mileage is charged on public networks, so roughly 3,600 miles, or about 947 kWh, is bought away from home.

If one public session in eight fails or is materially disrupted, and each disrupted session adds a five-mile detour at 3.8 miles per kWh, the extra energy is modest on paper. The real cost emerges when the detour also triggers a second connection fee, a higher tariff at the replacement charger, and twenty minutes of lost time. At an illustrative public rate of 79p per kWh, a five-mile detour uses about 1.3 kWh, or roughly £1.03 of energy. Add a 50p connection fee at the replacement unit and a £5 value on twenty minutes of time, and the cost of one disrupted session is closer to £6.50. Across roughly thirty disrupted sessions a year, that is around £195 before any contingency top-up is counted.

The figures are illustrative, not a forecast for every driver. But the structure holds: failed sessions are not free. They convert a published pence-per-kWh rate into a higher effective cost per delivered mile.

The contingency premium

When a planned charge fails, drivers rarely abandon the journey. They buy certainty at the next available point. That often means a motorway rapid charger rather than a cheaper destination unit, or a supermarket charger with a higher idle fee because the driver is now rushing.

The premium is the difference between the planned rate and the fallback rate, multiplied by the energy that must be replaced. If a driver planned to buy 30 kWh at 69p but instead buys 20 kWh at 85p after a partial failure, the fallback alone adds £3.20. Add the wasted energy already purchased at the failed site and the true cost of the disruption rises further.

App and payment fragmentation compounds the problem. Drivers who keep multiple network apps for coverage may pay subscription fees or lose access to member rates when using a guest payment route. A failed session can also leave a pre-authorisation hold in place for several days, which is a cash-flow cost rather than a direct charge, but it is still a cost to the driver.

Time is part of the tariff

UK public charging debates tend to focus on pence per kWh because it is comparable and visible. Time is harder to standardise but no less real. A failed rapid charge during a working day can cost far more in lost productivity than the electricity itself. For a driver who values an hour at £15, twenty minutes is £5; for a tradesperson with a booked job, it may be considerably more.

The practical implication is that reliability should be priced alongside rate. A slightly more expensive network that consistently starts first time may be cheaper overall than a budget network that requires a second attempt. That is not a defence of high tariffs; it is an argument for comparing delivered cost rather than advertised cost.

Translating reliability into pence per mile

For the illustrative driver above, £195 of disruption costs spread across 12,000 miles is about 1.6p per mile. If contingency top-ups and app fees add another £60 a year, the penalty approaches 2.1p per mile. On a home tariff of around 7p per kWh, that is a material addition to the running-cost picture, even though it never appears on a charging receipt.

Drivers can reduce the penalty without pretending failures do not happen. Checking live status before committing to a detour, keeping a RFID card as a backup to app payment, avoiding sites with a single rapid unit where an alternative is close by, and reporting faults with the unit identifier all help. None of these measures eliminates unreliability, but they lower the cost of encountering it.

The broader point for 2026 is that public charging comparisons should be honest about the difference between nominal and delivered cost. The kWh that flows is only part of the bill. The sessions that fail are paid for too, in time, detours and fallback tariffs. A reliability discount is not a discount at all; it is a surcharge that drivers absorb every time a charge point does not do what it promised.