Janet Oosthuysen, prospective Parliamentary candidate for Calder Valley, was chosen ahead of Cherie Blair's stepmother, Steph Booth, by Labour Party members last month at a hustings in Halifax.

Only a handful of votes separated the rival candidates.

Yesterday West Yorkshire Police confirmed that in April last year the divorced mother of three teenage children had scratched the bodywork of 44-year-old Craig Moore's BMW 320 car.

The incident happened close to the Fox and Goose pub at the bottom of Heptonstall Road, Hebden Bridge.

A police spokesman said: ''She was interviewed on June 2 and made a full admission and was subsequently cautioned a week later.''

Last night the contrite Hebden Royd town councillor said: "The end of this relationship was a very difficult part of my life. I'm not afraid to admit that I genuinely regret this incident; however, everyone makes mistakes.

"I co-operated fully with the police at the time of the incident and I now regard the matter to be closed."

Ms Oosthuysen, who was born in South Africa, hopes to replace Chris McCafferty as Labour MP for the Calder Valley at the next general election.

But some members of the Labour Party in Calderdale are unhappy with her behaviour.

One, who did not want to be named, claimed that if the matter had come to light before the vote Mrs Booth might well have triumphed instead.

She said: "What she did shows poor judgment.

"The vote was very tight and if this information had been available beforehand it could have changed the way in which at least half-a-dozen people voted – probably more.''

It is unclear what impact the revelation of Ms Oosthuysen's vandalism will have on Labour Party bosses when she is interviewed by them later this year.

Candidates already chosen to stand against her at the next general election include Conservative Craig Whittaker and Liberal Democrat Hilary Myers.