Perrior, who left her role in April after the Prime Minister announced the snap election, said that regarding the social care proposals, "it was the selling of it that was the problem".
The Conservatives received much criticism around the proposal to have no cap on how much people might pay for social care. May later said there would be a cap, leading to accusations of a 'u-turn'.
Perrior wrote: "I sat in too many meetings in Downing Street talking about the frontline problems of social care and the NHS not to have huge respect for the effort to tackle this issue head on without ducking the costs.
"But policies like this need weeks of warming up journalists, charities and industry leaders – not whacked out in a manifesto and briefed the night before."
Her comments come as new opinion polls show a narrowing of the Conservative’s lead. A YouGov poll published on Thursday (1 June) puts the party on 42 per cent and Labour on 39 per cent.
In her Times column, Perrior suggested the Conservatives should have done more to dampen down optimistic predictions about the extent of the party’s victory on 8 June.
"The truth is that the internal expectations when deciding to call an election in the first place were considerable more modest – a 50-seat majority was seen as a great success story. How on earth did we get so quickly to such sky-high numbers as 150?
"The smart thing to do would have been to ensure that the internal predictions were ‘leaked’ to let the air out of the balloon in a controlled manner. We should remind ourselves that voters don’t like gifting politicians a landslide and are wary of any whiff of arrogance."
Perrior is a veteran comms professional within Conservative circles, having worked on Boris Johnson’s successful London mayoral bid and been a senior media advisor to May when she was party chairman, and later to David Davis as shadow home secretary. She also founded the PR agency iNHouse with Jo Tanner.