The Tories’ chief executive and treasurer Mick Davis has resigned from his party roles, citing the need for a new team under Boris Johnson.

Davis’s decision to quit came as the chief executive of the London Chamber of Commerce, David Frost, resigned from his post to take up the role as EU adviser to the new Prime Minister.

In a letter to Tory party donors, Davis, who was the chief executive of multinational mining company Xstrata before it merged with Glencore, said he was resigning as CEO, treasurer and member of the Conservative party board with immediate effect.

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“I have so much enjoyed my time as treasurer and CEO, but circumstances change and I think that our new leader, Boris Johnson, should be free to choose a team at CCHQ who can work together to ensure that this organisation realises its central purpose – a clear and decisive victory at the next general election,” he wrote.

Davis urged party members to “get behind” Johnson and keep funding the party to prepare for a general election, which could happen in the autumn if Johnson fails to get a new Brexit deal or a no-deal Brexit through parliament.

“Our business plan has been carefully designed to achieve that goal but it needs to be properly executed and this is where you come in.

“Your support for the party and for me is deeply appreciated. But our plan needs to be properly financed on an ongoing basis and as our most important donors I am writing to ask you to get behind our new leader, Boris Johnson, and make sure CCHQ can deliver.

“Good politics is not a cheap exercise and if we are not properly resourced and financed we will risk a very bad outcome – Jeremy Corbyn in Number 10.”

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In his letter, Davis said one of his “great bugbears” had been the lack of unity in the party, adding: “Divided parties do not win elections.”

“Brexit with all its complexities and associated dogmas provides the unfortunate backdrop for division but if we are to effectively stand against the frightening threat of a Corbyn-led Labour government we all must find a basis of coming together.”