Confidence in the elections watchdog is evaporating as it emerged that almost half of its board have made public statements criticising the pro-Brexit campaign or backing calls for the result to be overturned, despite strict impartiality rules.

An investigation by The Sunday Telegraph found that four of the Electoral Commission’s 10 commissioners, including the chairman, had made pronouncements on Brexit since the referendum – all of them backing Remain.

The body’s code of conduct states that commissioners must “act at all times” to “uphold its impartiality”.

It led to calls for the commissioners to resign, as MPs suggested their personal views could have been behind the Commission’s refusal to investigate alleged illicit collusion by pro-Remain campaign groups, while conducting several inquiries into the official Leave campaign.

In three cases, the comments about Brexit were made while the commissioners were in post.

In the fourth, speaking months after being nominated as the body’s next chairman, Sir John Holmes said in a speech that he “regret[ted] the result of the referendum”, and complained about “the panoply of Eurosceptic nonsense about the EU” heard during the campaign.