Lord Heseltine criticised Mrs May's announcement as he said the Prime Minister had no "long term" future as Tory leader.
She was seen as having squandered the Conservatives' slender majority - and she had made clear at a meeting of backbenchers after the general election that she would only stay on for as long as her party wanted her.
Speaking on BBC Radio 5Live's Pienaar's Politics, Oliver - who quit Downing Street after being on the losing side of the referendum vote - said: "I was genuinely surprised to hear it and I was also genuinely surprised that a lot of the commentary that went around it was people saying 'well, what do you expect?"
In the immediate aftermath, several MPs called on her to re-consider her position and former Chancellor George Osborne, who has become a newspaper editor after being sacked by May, even said that she was a "dead woman walking". She could have said: 'I'm in Japan trying to get to a situation to make sure we have a proper trade deal with them when we leave the EU.
Margaret Thatcher was a month from leading the Conservatives to their third election victory when she produced one of her most famous phrases.
The Prime Minister told Political Correspondent Carl Dinnen she was "in this for the long term" amid speculation about her future in the role.
Ms May's comments follow a bruising summer in which rival camps among her cabinet have lobbied for a rethink of vital aspects of her policies on Brexit.
"Yes, there has been an terrible lot of speculation about my future which has no basis in it whatsoever", she told Dinnen, adding: "I'm in this for the long term".
"Not the politics, running the country, and she does a good job".
But instead of increasing her authority, damaged by the June election, she attracted derision from critics in her own party as well as the opposition.
But she rejected the talk of her standing down or being replaced in Number 10.
Few Conservatives dare risk doing anything that might trigger an early parliamentary election and hand a chance of victory to Corbyn.
"Serving PM will lead party into next election" should - journalistically - be a run-of-the-mill "dog bites man" story, not "man bites dog". "If she comes out of it with jobs up, and is seen to have told the European Union to get off and prospects are good. well you can go hero to zero and vice versa".