The two great British political parties Tuesday night pronounced on that burning question: What relations are allowed a legislator outside the marriage bed?

The Conservatives decreed that a divorced man can escort leading beauties around town, even if he makes the gossip columns. So Nicholas Scott, widely regarded as one of the ablest and most liberal Tory members of Parliament, beat back an effort to oust him from his Chelsea seat here.

But in Northampton, the local Labor Party ruled that a woman may not leave her husband for anothere woman. So Maureen Colquhoun, a left-wing campaigner for womens rights, was ordered to "stand down" at the next election.

According to veteran observers of Britain's politico-sexual life, however, the trouble both MP's got into reflects a much older rule: Do what you please in private but don't let it become public.

Mrs. Colquhoun - she insists that the Speaker of the House address her this way - she knew was in trouble when the newspapers reported that she had walked out on her husband of 26 years to live with Barbarra Todd, a former editor of "Sappho," a magazine for lesbians.

The couple sent out invitations to a housewarming picturing a pair of interwined females labeled "Maureen" and "Babs" and that, too, got into the press.

All of it was too much for the managers of the Northampton Labor Party, especially in a marginal seat. By a vote of 23-18, they told Ms. Colquhoun she must go because of her "recent statements and public behavior." They were also unhappy because she had slugged a parking-lot attendant who broke the roof of her car and snapped off her radio aerial. But the real complaint was Colquhoun's lesbianism.

After the meeting, the 49-year-old legislator denounced "the most disgraceful set of charges any person should have to listen to.

"I am gay," she said, "and I am proud of my pirvate life. I am glad to have the love and care of someone. My sexuality has nothing to do with my ability as an MP."

Colquhoun, the mother of three grown children, has a slim chance of being nominated again. She is appealing the local party's decision to Labor's national executive board.

The Scott affair for the Ihelsea Torries was a mix of both public and private life. Briefly a junior minister in Edward Heath's last government, the 44-year-old Scott is well to the left of his local party chiefs. But it was largely his divorce of 14 months ago and his role as man-about-town that got him into hot water.

Scott's wife successfully sued him for adultery, complaining of several affairs. More recently, he has appeared in the columns squiring some of London's most fashionable women, including Lady Charlotte Curzon and Cecelia Tapsell, the ex-wife of another MP.

All this aroused the wrathe of Neville Beale, chairman of the Chelses Conservative Association. He urged the party to take another look at the man.

Scott had a lot going for him. Powerful Tories in the party's Heath wing privately and publicly backed him.

Cherry Hughes, a Tory Praty worker whom Scott had dated, told the Daily Express that he had a " a marvelous soft quality that gets the girs." But this may have hurt Scott more than it helped.

A. R. Whitaker, and umpire with the Lords and Commons cricket team, wrote The London Times that Scott is "one of the leading batsmen" for the club and "It is therefore unthinkable that he should be dislodged by his constituency."

it worked. Scott was re-endorsed, 69-21.

Even before the results were in, the analysts were figuring out what it all means. In The guardian, Polly Toyobee charged that Coluquhoun was a victim of male charvinism since the House has always tolerated homosexuals without difficulty.

Stuff and nonsense, retorted Andrew Roth, author of the much-respected weekly newsletter, "Westminster Confidential." Homesexual MPs, Roth observed, usually come equipped with a wife as "cover." Colquhoun had foolishly shed her cover and in public.