Drivers who were convicted of speeding on the M42 motorway may be able to challenge the conviction.
The warning comes after the Crown Prosecution Service alerted Warwickshire Police to the fact that the font used to display variable speed limits on some signs may not comply with traffic regulations, as they were taller and narrower than they should have been.
The non-compliance spanned over six years and some are calling for the speeding convictions on that stretch of the motorway to be quashed as they may be unenforceable.
Once Police were informed, they stopped using the signs as a means of enforcement and dropped prosecutions they were intending to pursue on the affected road.
It has been reported that at least 11,000 fixed penalties were issued to motorists breaking the variable speed limit between junctions seven and nine of the M42 last year.
The Department for Transport has since granted authorisation for all the signs and Warwickshire Police started enforcing variable speed limits again on those sections of the M42 on 1 Jan 2013.
By Sean Joyce
If you are a motorist facing a speeding prosecution, contact our team of motoring offences solicitors today - 0845 00 20736.