Welsh motorists living under the country's new blanket 20mph zones will actually be able to drive at 25mph before falling foul of new laws.
The default 20mph speed limit in built-up areas in Wales will be enforced from today and the Welsh government has confirmed motorists will face sanctions if they exceed the limit.
However GoSafe Wales, which connects the Welsh police and local authorities together in a road safety network has said that the enforcement of fines will only begin at 10 percent of the speed limit plus 4mph.
This means in practice that drivers in Wales will only be prosecuted if they are caught driving above 25mph in a 20mph zone.
This is more leeway than is given to other drivers in Britain where motorists are subject to an enforcement threshold of 10 per cent plus 2mph, making the limit for a 20mph zone 23mph.
It comes as pro-motorist groups label the new 20mph limit 'unenforceable', and question why the policy was introduced in the first place if drivers will still be allowed to reach speeds of 25mph before being slapped with a fine or points.
But ministers said not all drivers breaking the 20mph limit will initially be prosecuted, just the most dangerous offenders.
Roadside teams will use speed monitoring equipment to catch offending motorists.
They will be stopped and given a choice between a fine and points, or roadside engagement.
Go Safe Wales has also said magistrates will only deal with excessive speeding of 40mph or more under the rollout. Ian Taylor, a director at the Alliance of british Drivers told MailOnline the policy could well be unenforceable due to costs.
He said: 'The lower you make the limit, the more difficult it is for people to actually keep to it and probably means they'll want to do it less anyway.
'This means there's always the potential there for prosecutions. As regards to them saying over 26mph for prosecutions, it's ironic as that is sort of the limit.
'They think that imposing 20 mile an hour limits brings the average speed down to but if it's 26mph regardless you wonder why they bothered!
'The whole policy could end up being unenforceable it depends how much it's liable to cost them to enforce it properly.
'Having said that if they enforce it enough, they might make the money they need to pay for it from the fines.'
Speaking to the Telegraph, Peter Fox, the Welsh Conservatives' minister for finance warned that the confusion was likely to result in more fines.
He said 'It's confusing out there especially if you are visiting Wales.
'With 20mph being the default limit, together with unclear and inconsistent signage, it would be easy to lose a licence in a day.'
MailOnline has approached GoSafe Wales for more information.
The Welsh scheme to reduce the default speed limit for 'restricted roads' from 30mph came into force in September, affecting 7,700 miles of road. It aims to cut deaths, noise and pollution and encourage people to walk or cycle.
There was confusion around when the new national speed limit would be enforced. It was said that enforcement would begin three months after the new speed limit was introduced, which would have been December 17 before the Welsh government confirmed the enforcement for the speed limit would begin in January.
The speed limit reduction to 20mph affects 'restricted roads' - those with 'street lights spaced no more than 200 yards apart, usually located in residential and built-up areas'.
Transport is a devolved matter so the Welsh government has made the change unilaterally.
According to its own impact assessment, the 'main economic dis-benefit' of the new regime 'relates to increased journey times from lower average vehicle speeds'.
It states that this could result in an economic hit of up to £9 billion over 30 years; the cost of implementing the scheme will be £33 million.
But Wales' First Minister Mark Drakeford said the 20mph speed limit would save lives and the cost was 'outweighed' by reduced impact on the NHS and emergency services.
Mr Drakeford has said 'the evidence is incontrovertible' that 'driving more slowly in built-up urban areas saves people's lives' and that it will save the Health Service £90million as a result.
He cited a similar scheme in Spain, saying it had cut urban deaths by 20 percent.
Critics say penalty fines will hit drivers who already face larger petrol bills for running their engines at lower - and less efficient - speeds.