Signs will carry metric measurements above imperial feet and inches, which could confuse motorists, critics fear

Road signs showing height and width limits are to carry metric as well as imperial measurements under Government plans.

Feet and inches will only be allowed on bridges, tunnels and narrow roads if metres are also used.

In a Department for Transport report ministers say they will ‘no longer prescribe imperial-only height and width limit signs’.

Examples given in draft legal orders show the metric measure takes precedence on top of signs – with imperial underneath.

Luke Bosdet, a spokesman for the AA, said this could be a recipe for confusion. ‘At the very least the UK measure in feet and inches should be on top, with the metric details below,’ he added.

‘Motorists and hauliers have got used to seeing signs in feet and inches. In fast moving traffic if they glance up and read the metric metres first, there could be a problem.

‘Putting metric measures on top and in a more prominent position is going too fast. The cost of digging out a truck stuck under a bridge or underpass because the driver misread the sign would be significant.’

The move was described as a ‘watershed moment’ by Neil Herron, the Sunderland fishmonger who became known as the ‘metric martyr’ for his campaign against kilos and grams.

He said: ‘It’s the first time metric measurements have been allowed on British road signs. Let’s hope it’s not the start of a slippery slope.

‘The last thing the British public would want is to see speed limits in kilometres per hour as on the Continent. Nor would they stand for distance signs in kilometres instead of miles.’

Details of the plan are buried away in a report on road sign regulations published by the Department for Transport and seen by the Daily Mail.

All new signs will carry both imperial and metric measurements as will any signs that are replaced. One theory – unconfirmed – is that the metric measures have been included to help foreign lorry drivers making deliveries in the UK.

Critics fear the changes are the start of a 'slippery slope' and that before long speed signs could be changed from miles per hour to kilometres per hour

The British public 'would not stand' for distance signs to be changed from miles to kilometres, if such a measure was brought in, critics said

The Government report is its response to a consultation on ‘The Traffic Signs Regulations and General Directions (TSRGD) 2015’ which looks at simplifying signs and removing clutter.

But tucked away under ‘other issues’ the report notes: ‘In order to improve road safety and compliance, ministers have decided that the revised TSRGD will no longer prescribe imperial-only height and width limit signs.

‘Imperial-only signs can remain in place only until such time that they become life-expired, or replaced during routine maintenance, at which time the dual-unit equivalent must be used.’

A Department for Transport spokesman said last night: ‘Displaying dual measures of height and width restrictions make it easier for drivers and are designed to help improve safety on our roads.’