Although he is well-known for his tough line on immigration, Terry Dicks has attributed his decision to leave the Hayes and Harlington seat to the local party's unwelcoming attitude.
"Sikhs are damn good Tories, hard-working people, yet they appear not to be welcome. I'd rather stand in a safe Labour seat," Mr Dicks says on BBC2's Around Westminster programme to be broadcast tomorrow.
More than 10 per cent of the electorate in Hayes and Harlington are black or Asian. Mr Dicks reckons that there are something like 10,000 Sikhs in the constituency and says that they have been "discouraged" from joining the party's association and the local Conservative club.
"I find that appalling. It's been going on for far too long and I won't have any part of it any more," he said.
However news of Mr Dicks' disenchantment with the seat he has represented since 1983 comes as no surprise. It is the most marginal Conservative constituency in the South-east, with a majority of just 53, and is the second most marginal in the country.
Mr Dicks, aged 58 and a plain-speaking right-winger, has joined what is known as the "chicken run" in search of a safer seat. In August he failed to win the candidature of St Ives, Cornwall.
"When we've had elections and Sikhs have helped me they've had to meet me in car parks and down the road and not come into the club," Mr Dicks says on the programme. "When we had a party to celebrate my victory I asked if they could be invited and the answer was 'no'."
The MP's charges were rejected last night by representatives of both the association and the Conservative club. Mary O'Connor, chairman of the association, said local Tories embraced everyone in exactly the same way.
The Conservative club secretary, Alex Freckleton, said: "I haven't seen him [Mr Dicks] in our club for years and years. I was the secretary of Southall cricket club for 17 years and I have a lot of very good friends who are Sikhs."
Describing Mr Dicks' claims as "rubbish", Mr Freckleton added: "So far as I am concerned there is no colour bar in the club. I have no colour prejudice at all."