David Cameron faced a Tory grassroots revolt over the European Union referendum, with local party chiefs complaining about his direction to MPs not to worry about their views on Brussels.
The Prime Minister was accused of showing "disrespect" to party activists in a letter signed by representatives from more than 40 local Conservative associations.
But in a boost to Mr Cameron, one of Margaret Thatcher's closest advisers suggested the former prime minister would have backed his proposed deal for a new relationship with Brussels.
Lord Powell of Bayswater, Mrs Thatcher's former private secretary and foreign affairs adviser, used a Sunday Times article to say that although the so-called Iron Lady might have "raged more mightily" at Brussels than Mr Cameron "she would have gone along with what is on offer, indeed negotiated something similar herself".
Europe has long been a source of division with the Tory ranks and the approaching referendum has threatened to deepen the splits.
The letter by local party chiefs to The Sunday Telegraph came in response to Mr Cameron's plea in the Commons for his MPs to ignore the views of their constituency associations when deciding on the EU question.
"Don't take a view because of what your constituency association might say, or you're worried about a boundary review, or you think it might be advantageous this way or that way," he told MPs on Wednesday.
In a letter to The Sunday Telegraph, the Conservative associations say Mr Cameron has "undermined" the goodwill that existed among loyal members and warned him: "No prime minister has a divine right to rule."
The missive is signed by 44 chairmen, executives, former chairmen and Tory activists, representing 43 local party associations across England, Wales, Scotland and Northern Ireland.
A Downing Street spokesman told the newspaper: "The PM has the greatest of respect for Conservative associations across the country. He was simply making the point that everyone should ultimately vote with their conscience."
Meanwhile, speculation continued to surround the likely positions of Cabinet ministers when the referendum campaign finally gets under way.
Reports suggested that employment minister Priti Patel is likely to back a Brexit, while The Sunday Telegraph claimed Mr Cameron had personally appealed to Justice Secretary Michael Gove not to join the campaign for the UK to sever ties with Brussels.
The Sunday Times reported that Work and Pensions Secretary Iain Duncan Smith, a prominent Eurosceptic expected to campaign for Brexit, had told friends Mr Cameron's deal was a "load of rubbish" which would be challenged in the European courts.
The confusion in the Brexit camp deepened as a third group indicated it was considering applying to be officially designated as the main Leave campaign.
Grassroots Out (Go) said it could seek the Electoral Commission designation, potentially fighting it out with Vote Leave and Leave.EU - although it has close links with that campaign.
Tory MP Tom Pursglove, co-founder of Go, said: "If we are going to win this crucial referendum for the future of our country, it is imperative that the current impasse, which is serving as an enormous distraction, must come to an end and it seems that there is a growing mood that GO could well be the vehicle to achieve this - indeed, we have been approached by many people in many parties, enquiring as to whether this might be possible."