The secret is out – it was the Royal Marines at Dartmouth who were the pranksters behind the infamous House of Commons 'cock' speech by MP Penny Mordaunt.

The MP for Portsmouth North hit the headlines when she launched into a Parliamentary speech about hen and cock welfare and continued with a diatribe loaded with double entendre references.

Now she has revealed that it was all down to a bet she made with a bunch of Royal Marines during a visit to the Britannia Royal Naval College.

The Conservative MP, who has since been made a junior communities minister, managed to squeeze the word 'cock' into the speech given to the Comm­ons in March about the welfare of poultry, six times and 'lay' or 'laid' five times.

But at an awards dinner last week, Ms Mordaunt, who is also a Royal Navy reservist, revealed it was all down to her losing a bet at the naval college. She was reported as saying: 'Some of my marine training officers at Dartmouth thought it would be a good idea to break my ladylike persona by getting me to yell particular rude words during the most gruelling part of our training.

'They failed but, during our mess dinner at the end of the course, I was fined for a misdemeanour.

'The fine was to say a particular word, an abbreviation of cockerel, several times during a speech on the floor of the Commons – and mention all the names of the officers present.'

Ms Mordaunt ended the speech with the line: 'When we eventually head into spring, let us have no cock-ups on hen welfare.'

There has been some backlash in the Commons over news of the bet.

Labour MP Kate Hoey accused Ms Mord­aunt, who also appear­ed on ITV reality show Splash! of trivialising Parliament, saying that the public 'expects' debates in the Commons to be on 'matters of serious concern'.

Ms Mordaunt MP was given the Speech of the Year award by the Tory-supporting Spectator magazine for her Loyal Address in June – an all-round better, and funnier, dialogue.

The Loyal Address is a 'reply' to the Queen's Speech following the State Opening of Parliament. Considered an honour given to two government backbenchers, the speeches are not contentious and often humourous, with flattering references to their constituencies.

Ms Mordaunt is only the second female MP to have given the Loyal Address to the Queen.

The MP said at the time of her visit to the BRNC in February: 'This was by far the most challenging exercise I've taken part in and you really felt that all the skills, knowledge and resilience you'd built up over training were being tested to the max.'