Police hidden in unmarked cars are to deploy a special laser device to catch lawbreakers.

The covert operation is part of the countywide crackdown by North Yorkshire police to nab speeding motorists, especially bikers, on Bank Holidays.

Autovision, a camera linked to a laser beam, is to be operated from unmarked cars.

And it will be deployed this weekend to make speed checks at identified blackspots.

Police have regularly targeted the A65, Skipton to Kendal road, which is popular with bikers from Bradford heading for Devil's Bridge at Kirkby Lonsdale.

Assistant Chief Constable David Collins said: "You won't see us but - trust me - we will see you. I prefer officers to carry out high visibility patrolling - it makes officers available to the public, and reassures people we are out there for them - but extreme speed calls for extreme measures."

The action is linked to Operation Halter, the hard-line policy adopted two years ago to combat rising motorcycle casualties.

It involves fast-tracking extreme speeders - those smashing limits by more than 30mph - through the courts.

It means people face a one in six chance of losing their licence within six weeks.

So far this year there have been 410 fatal or serious injury accidents involving cars or motorcycles - a reduction of 7.6 per cent on the same period last year.

Motorcycle rider deaths so far this year are 11 - the same as 2004.

But the total motorcycle crashes in which someone was killed or seriously injured number 94, down from last year's 105.

Mr Collins said: "Ninety-four is still too many. Operation Halter goes on. We should not and will not accept the appalling death toll on our roads."

During Operation Halter so far this year:

l 478 speeders have been caught, compared with 159 in 2004

l 194 extreme speeders have been or are being fast-tracked to court. A third of them are motorcyclists.

l 69 fast-trackers have already been convicted and almost 30 per cent of them - riders and drivers - have been disqualified quickly.

l 74 riders have been caught crossing double white lines, compared to 19 this time last year

Officers will be deployed in cars, vans and motorcycles, both plain and marked.