A senior Conservative MP under scrutiny over his extra earnings for legal work has defended himself – and declared it is up to his constituents to vote him out if they are unhappy about it.

Sir Geoffrey Cox’s entry in the register of members’ interests shows he earned more than £800,000 for law firm Withers, which is representing the British Virgin Islands government in a corruption case brought by the UK government.

It has been revealed that he voted by proxy in the House of Commons while earning hundreds of thousands of pounds for the legal work more than 4,000 miles away in the Caribbean.

Sir Geoffrey is also facing claims that he used his parliamentary office to undertake some of his work for Withers.

The MPs code of conduct states any facilities “provided from the public purse” are used “always in support of their parliamentary duties”, adding: “It should not confer any undue financial benefit on themselves”.

But in a statement posted on his website Sir Geoffrey said “he does not believe that he breached the rules” and claimed he consulted the Conservative chief whip about voting by proxy while in the Caribbean and “was advised that it was appropriate”.

He describes himself as a “leading barrister in England” who “makes no secret of his professional activities”.

It continued: “Sir Geoffrey’s view is that it is up to the electors of Torridge and West Devon whether or not they vote for someone who is a senior and distinguished professional in his field and who still practises that profession.

“That has been the consistent view of the local Conservative Association and although at every election his political opponents have sought to make a prominent issue of his professional practice, it has so far been the consistent view of the voters of Torridge and West Devon.

“Sir Geoffrey is very content to abide by their decision”.