John Major's former press secretary says the EU row engulfing David Cameron has "depressing" echoes of the 1990s.
Sheila Gunn urged Tory rebels to "show some common sense" and said the party risked handing election victory to Labour.
She also savaged the new crop of Tory MPs, saying they were disloyal and not willing to knuckle down for the good of the party.
Cameron has promised a referendum on Britain's membership of the EU in the next Parliament - but rebel MPs are calling for immediate legislation to set it in stone.
Over the weekend, Cabinet Minsisters Michael Gove and Philip Hammond said they would vote to leave the EU if a referendum was held tomorrow.
Gunn, who was Major's press secretary from 1995 to 1997 and advised him in the run-up to the 1997 General Election, told The Huffington Post UK: "Yes, there are some parallels with the back end of John Major's premiership.
"One of the differences is, that was when the Conservatives had been in power for 17 or 18 years. Now the Conservatives have only been in power in coalition for two or three years.
"I would really expect the Conservative MPs to show some common sense. I understand they have strong feelings on the matter, but is now really the right time to make a fuss of it?"
Gunn, now an author and lecturer in political journalism, said Ukip's success in the recent local elections had been "a protest vote" that was due more to immigration concerns than anti-EU sentiment.
She added: "I still probably have the sores from when I worked with John Major, when Conservative MPs would say, 'oh, but Sheila, this issue is much more important than everything else' - but they were just handing victory to Tony Blair and the Labour Party.
"You could also say now that the Conservative Party is handing the election to the Labour Party."
While there have been rumblings from Tory grandees like Michael Portillo and Nigel Lawson, Gunn said a lot of the rebels were new MPs, and criticised the party's new intake.
"It is worrying, because normally you punish them by never giving them ministerial office...and they do not seem very frightened of the whip," she said.
"A lot of them have achieved a lot in their lives before Westminster, so coming into Parliament they do not want to spend their time answering questions about dustbin collections and school places.
"It's much more personality politics. To win the next election, they have to look and act like a team.
"I do find it very depressing. There are too many echoes of what happened at the end of John Major's government."
Not enough of the recent Tory intake have good "political judgement", she said.
"They should learn more of that and spend less time knocking the party."
There are very clear echoes of the disloyalty of some of the Conservative MPs who think that their ideas of politics are more important than actually backing their leader and acting as good team players."