And when County Hall agreed to install signs to stop vehicles using Darkinson Lane, Black Lane and Ash Lane as a rat-run, it was considered at least a step in the right direction.

But today it was revealed the signs are completely pointless – because council workers have put different width restrictions on them.

One sign, near Lea Lane's junction with Back Lane, says vehicles more than 6ft 6ins wide cannot use the stretch. But just up the road at Darkinson Lane, the signs gives the width restriction as 6ft. A third sign in Ash Lane also displays 6ft.

The blunder comes just days after council workers painted zig zag lines to keep traffic away from the entrance of Holme Slack Community Primary – hundreds of yards away from the school.

Sgt Dennis Nicholson, of Preston's road traffic policing unit, said: "We are not prepared to enforce them if one of them does not comply with the other two. Effectively, someone could commit an offence going in, but not coming out. We have notified the county council and it is in hand."

The gaffe has reignited a nine-month row over the signs. Residents now want all the signs to be replaced with signs simply saying 'access only' to stop all but residents' vehicles using the roads.

Police say they would not oppose that move, but the signs would also be unenforceable.

Sgt Nicholson said: "We would not be there to see people. We can't stay down there monitoring the signs."

But Preston West County Coun Norman Abram said residents believed the signs could work by discouraging drivers from using the roads. He said: "Why not scrub the width restrictions and say 'access only'? By doing that they would make 70-odd people happy."

A spokesman for Lancashire County Council said the errant sign would be replaced.

"What we intend to do is put a fresh set of numbers on the sign, so it would not be a new sign, so the cost would be pounds."

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