One of the most senior members of the Conservative party will enter into a civil partnership today.

Up to 300 people are thought to have been invited to a celebration of Alan Duncan’s nuptials at Merchant Taylors’ Hall in London.

Conservatives will be in jubilant mood after the government’s crushing defeat in yesterday’s Glasgow East by-election. The SNP took Labour’s third safest seat in Scotland with a 22 per cent swing.

There is speculation that former Tory leader Lady Thatcher and the current occupant of that job, David Cameron, will be in attendance.

After a whirlwind 14-month romance Mr Duncan has proposed to his boyfriend on Valentine’s Day during a holiday in Oman.

He met 39-year-old James Dunseath at a dinner arranged by friends.

Mr Duncan, 51, is the Shadow Secretary of State for Business, Enterprise and Regulatory Reform and has been MP for Rutland and Melton since 1992.

He is the first Tory MP and the first member of either the Cabinet or Shadow Cabinet to enter into a civil partnership.

He came 15th on the PinkNews.co.uk list of the 50 most powerful LGBT people in British politics published in December.

“Compact, suave and beautifully presented, Alan Duncan is the liberal, urbane face of the Conservative party,” his citation read.

“He became the first Tory MP to voluntarily come out, in 2002, has been a frontbench presence for nearly a decade and is a nimble Commons performer.

“Duncan has a devoted following among some gay Tories, and he has certainly spoken up in favour of gay rights, often disagreeing, politely, with many of his own colleagues.

“His style and politics sit well with Cameron, and he can expect to retain a high profile presence on the frontbench.”

If Mr Cameron attends today’s civil partnership ceremony it will be the first he has gone to.

Mr Duncan and Mr Dunseath announced their intention to enter into a partnership in the Court Social page of the Daily Telegraph.

“We hit it off instantly and our friends say we are inseparable,” Mr Dunseath told the paper in March.

“He may be a politician but he’s great fun. We both feel it’s so right and we’re very lucky.”