Hundreds of thousands of unlicensed vehicles are being driven on UK roads, official figures show.
Data published by the Department for Transport (DfT) shows an estimated 634,000 vehicles are being used, despite their vehicle excise duty (VED) not being paid.
This represents 1.6% of all vehicles in UK traffic, down from 1.8% in 2017.
Some 46% of vehicles being used with no VED have been untaxed for more than two months, suggesting there is a persistent minority of motorists who are intentionally not taxing their vehicles.
Lost revenue from non-payment of VED has soared since the abolition of the paper tax disc in October 2014.
Figures for Britain show the potential total has risen from £35 million in 2013/14 to £85 million in 2019/20.
Abolishing the paper disc removed the visual in-vehicle reminder of the expiry date for VED, although notifications are sent by the Driver and Vehicle Licensing Agency (DVLA).
The Government said at the time that the decision would eventually save the DVLA about £7 million a year.
Every vehicle registered in the UK must be taxed if it is driven or parked on a public road.
Steve Gooding, director of the RAC Foundation, said: “Despite the recent slight fall in evasion, the rate is still far higher in this age of digital renewal than back when motorists received a paper disc to display to prove they’d paid.
“VED evasion doesn’t just short-change government, in the future it will also lead to worse highways.
“Ministers have previously committed to ring-fencing VED revenue for spending on our major roads, and judging by the state of the network, we need the Treasury to collect every single penny that’s due.
“There’s also a safety issue, because when we pay we are prompted to check that we have motor insurance, and that vehicles over three years old have a valid MOT.”
The DfT noted that some of the potential lost revenue is recovered through DVLA enforcement action, or by payments being made at a later date.