A convoy of defiant truckers last night appealed to motorists to join their fight for a big cut in fuel duty after completing the third leg of their go-slow protest journey from the North-East to London.

Twenty hauliers and farmers and ten car drivers, who vowed to complete their journey to the capital, took just over two hours to travel 57 miles from Cannock, Staffordshire, to a truck stop on the A5 near Rugby, Warwickshire.

It came as Defence Secretary Geoff Hoon insisted security concerns over possible terrorist infiltration of the convoy were "real", only hours after it emerged a massive car bomb discovered in Belfast was destined for London.

The protestors have been told they will not be allowed to bring their trucks into London when they near the end of their journey from the North-East tomorrow.

Yesterday, the vehicles, including two wagons carrying tractors, were cheered by dozens of supporters, some waving Union Flags, from motorway bridges as they drove along the M6 through the West Midlands, Warwickshire and Leicestershire at 30 to 40mph.

The fuel protest convoy, which followed a route prescribed by police, then travelled south on the M1 into Northamptonshire before joining the A5 northbound and re-entering Warwickshire.

Protestors were served with notices under the Public Order Act 1986 prior to yesterday's "procession", instructing them to comply with traffic laws or face arrest.

Ford Fiesta driver Tony Finlay, 28, of Sacriston, County Durham, implored other motorists to join the protest.

The warehouse worker, who intends to follow the convoy to London, said: "The price of fuel is so diabolical that a friend of mine couldn't afford to run his lawnmower and he had such a big garden he had to sell it.

"People don't seem to realise that car drivers can join the protest - they think it's just for truckers, which it's not."

The convoy is being tailed by an environmentally-friendly Greenpeace campaign lorry, and members of Friends of the Earth demonstrated against the truckers as they passed Great Barr, Birmingham