Lord Tebbit is a long-time critic of David Cameron
David Cameron must promise a referendum on whether the UK should leave the European Union, former Tory chairman Lord Tebbit is expected to say.
In a speech on Monday, he will call on the Conservative leader to show "Thatcherite courage" on the issue.
This should happen "within two years" of a Tory election win, he will add.
The speech marks the 20th anniversary of an address in the Belgian city of Bruges in which Baroness Thatcher warned of a European "super state".
Lord Tebbit, a leading Eurosceptic who has criticised Mr Cameron on several occasions since he became party leader in 2005, will speak at a dinner in London in honour of - and attended by - the former prime minister.
We cannot drift on as we have been
He will say: "I hope that the Conservative Party will set out a negotiating brief that the next Conservative government will take to Brussels early in its next term, and that it would, within two years of the next election, present to the British people the outcome of its negotiations.
"Then, in a referendum, the British people would decide whether to accept what was on offer - or simply to leave the union.
"We cannot drift on as we have been. It is not fair either to the British people or to the European Union.
"We need to show Thatcherite courage and determination to lead the country along that path."
Czech president Vaclav Klaus will also address the event and is expected to say: "The marching towards an ever-closer union must be reversed.
"We need to continue fighting vigorously for the goals outlined in the Bruges Speech, just as Lady Thatcher always has."
In her 1988 speech, the then prime minister declared: "We have not successfully rolled back the frontiers of the state in Britain, only to see them re-imposed at a European level, with a European super state exercising a new dominance from Brussels."
Of the main political parties, only the Liberal Democrats are pushing for a referendum on whether EU membership should continue.
Baroness Thatcher, who turned 83 earlier this month, has kept a low profile in recent years after her doctor advised her to stop making public speeches on health grounds.
She visited Downing Street as a guest of Prime Minister Gordon Brown in September last year.