The police and Ministry of Defence have stepped in to help the teenage organiser of a mass motorbike ride through Wootton Bassett in aid of servicemen and women.

Elizabeth Stevens, 18, of Luton, planned the ride on March 14 with a few friends but, through the social networking website Facebook, the numbers of bikers and pillion passengers expected to take part has reached 14,000.

Now registration for the ride has been closed early to stop numbers swelling to unmanageable levels and the start of the rally has been switched from Leigh Delamere services on the M4 to Hullavington Airfield.

Miss Stevens, who is being helped by Julia Stevenson, a pensioner biker from Kent, have agreed with Wiltshire Police to an amended route from Hullavington through Brinkworth and along the A3102 to Wootton Bassett.

The police involvement follows fears of mayhem in the town as the bikers ride through.

Miss Stevenson said: “The logistics have been a nightmare.

“It has been crazy but with the help of the police, the MoD and the Army it has come together.”

She added: “The police have been wonderful and nothing has been too much trouble for them.

“I feel honoured to work with them. It is wonderful that everybody is just coming together and supporting our troops.

Sergeant Jo Spencer from Wootton Bassett police said: “It has become evident to them that they do need our advice to help them proceed. I don’t think they realised the power of Facebook.”

Singer Tim Pitman will perform onstage at Hullavington and a cheque will be presented to the Afghan Heroes charity.

Councillors had been concerned about the impact of the rally on Wootton Bassett. But Coun Chris Wannell said: “I have every faith in the police in dealing with this issue and I think we should leave it to the authorities.”

Chief Inspector Owen Gillard said: “We fully support Afghan Heroes and the excellent work that they do. It’s wonderful to see so many bikers registered to take part for such a worthy cause.”

But he warned motorists to expect delays on March 14.