A Brexit assessment by Scott Wightman, right, the high commissioner to Singapore, was leaked to Politico

Concerns about breaches of diplomatic confidentiality are growing after it emerged that a British envoy in Singapore had also been the target of a leak.

A critical confidential assessment of the impact of Brexit by Scott Wightman, the high commissioner, has been disclosed in another breach undermining the UK’s time-honoured diplomatic code.

The breach did not receive the same level of scrutiny as the leak of cables from Sir Kim Darroch, the ambassador to Washington who had to resign last week over the affair, but it is now being seen as part of a pattern of a breakdown of trust in Whitehall prompted by the political pressures of Brexit.

In his final message before leaving his post, Mr Wightman, a former ambassador to South