The first openly gay Conservative cabinet minister has said coming out was "like going 15 rounds with Mike Tyson".

In his first interview since announcing he was gay, Scottish secretary David Mundell told ITV he had thought that it would be worse than facing SNP MPs in parliament, but he was glad he had done it.

Mundell told ITV's Paul Brand for Around the House: "I've said I thought it would be more difficult than standing up at the Despatch Box in the House of Commons against my 56 SNP colleagues. In fact, it wasn't... although I did find it very emotionally draining. I felt, the day after, that I'd gone 15 rounds with Mike Tyson.

"I hadn't really understood the reaction", he said. "I expected a positive reaction from certain people, but what I got was from lots of people I'd not met, who came back with personal stories."

The MP for Dumfriesshire, Clydesdale and Tweeddale also said he had received a very positive reaction from Prime Minister David Cameron, who "stopped eating his apple" when Mundell said he had something personal to tell him.

"He stopped eating his apple, so I don't know what he thought I was going to say to him!" But the reaction was positive. "He said 'well done' and 'good on you' and 'we'll support and help you whatever.'"

He added: "[I thought] other people have to tell their mum and dad – I had to tell the Prime Minister."

After he made the announcement, Mundell said colleagues came up to congratulate him – demonstrating how far things have come for LGBT people since Mundell's childhood, when being gay was still a criminal offence in Scotland.