The group was sprayed with loose road chippings as lorries passed

Her husband Michael said the incidents happened as the cyclists travelled through the state of Colorado.

A lorry also moved into the middle of the road as it passed to "deliberately" spray the riders with loose chippings to try and injure them, he said.

Mrs Tomlinson, 42, is cycling 4,200 miles from San Francisco to New York.

In his blog on the BBC website, Mr Tomlinson described how the group was sprayed with road chippings by the lorry, before being followed for 90 minutes by a police car.

They were eventually pulled over and told to cycle on the hard shoulder, he said.

"The shoulder was a narrow strip of road mainly containing debris and would have caused numerous punctures and would have been dangerous," said Mr Tomlinson.

The ride began at the Golden Gate Bridge in San Francisco on 29 June

"The police officer was belligerent and not wanting to be arrested we agreed with him, so as not to give him an excuse for further action; his manner was spoiling for a fight; courtesy was at a minimum, it was certainly not a pleasant experience."

Later, the occupant of a pick-up truck threw a Coke bottle at Mrs Tomlinson and the other cyclists.

Mr Tomlinson said: "Who needs to encounter these sorts of people when cycling; whatever the cause or whoever the person is?

"Our initial experience of Colorado has not been good but let's hope they live up to their reputation of being a cycle-friendly state."

Mrs Tomlinson, who was diagnosed with advanced metatastic breast cancer in 2000, has suffered from dehydration, extreme fatigue and back pain during the marathon bike ride.

Her aim is to raise �1,250,000 for UK and American-based cancer and children's charities.

She is joined on the 62-day trip by Leeds Metropolitan University lecturer Ryan Bowd, 27, of Calgary, Canada, and 40-year-old Martyn Hollingworth from Huddersfield, West Yorkshire.