Sir Peter Westmacott also suggested leaker of Sir Kim Darroch's private memos would now be caught.
The Metropolitan Police say they “respect the rights of the media” but believe the breach may have “no public interest defence”
Sir Kim Darroch, the UK's ambassador to the US, resigned earlier this week after private comments became public.
But Tory leadership tells BBC's Andrew Neil his comments were "misrepresented" to the ambassador.
Sir Kim is just the latest senior civil servant to be targeted for not serving a narrow political agenda, the FDA's Dave Penman writes
"He literally doesn’t understand what diplomats do." Critics round on Brexit Party MEP after Newsnight appearance.
The five things you need to know about politics today
From throwing Kim Darroch 'under a bus' to bungling the case of Nazanin Zaghari-Ratcliffe, this is what we should expect from a Johnson premiership, writes journalist Anthony Harwood
Anatomy of a resignation: How the Washington ambassador decided his role was untenable after facing the wrath of Donald Trump.
Sir Kim Darroch, Britain’s ambassador to the US, has resigned after leaked diplomatic cables revealed a blistering critique of President Donald Trump and his administration. In a statement issued on 10 July, Darroch said it was now “impossible” for him to do his job. He leaves his position after three years as ambassador to the US.