Scottish National Party MPs are threatening to refuse to agree to a new code of conduct in the House of Commons that forces them to work in the best interests of the United Kingdom, despite the party’s policy to break it up.

A new draft code of conduct that governs the work of MPs has changed one of the key duties of MPs to require them to “have a duty to act in the interests of the United Kingdom as a whole”.

The previous code, which only came into force last year, required MPs merely to have “a general duty to act in the interests of the nation as a whole”.

Some SNP MPs – whose founding aim is to create an independent Scotland - are now threatening to vote against the code of conduct unless it is changed by Kathryn Hudson, the standards commissioner.

The code will be considered formally by the House of Commons standards committee after a seven-week consultation, which ends next month.

Tommy Sheppard, an SNP member of the committee, said: “We will be seeking to get it changed – we were elected on a democratic mandate to reform the UK out of existence.