Teresa Gorman, a leading Conservative rebel over the Maastricht Treaty in the 1990s, has died aged 83, her family have said.
A former MP for Billericay in Essex, Ms Gorman trained as a teacher before being elected in 1987.
She was a prominent figure in the rebellions over Europe that nearly brought down John Major's government.
She had the Conservative whip withdrawn for refusing to back the EC Finance Bill in 1994.
Regarded as a talented but maverick politician, Ms Gorman was also known for her public enthusiasm for hormone replacement therapy (HRT).
In recent years, she shifted her allegiance to UKIP, and voted for the party at the general election in May.
She held the Billericay seat until 2001.
MAASTRICHT TREATY
The Maastricht Treaty, which came into force in November 1993, was also the blueprint for what was to be Europe's biggest project for the next decade - economic and monetary union.
It defined the three stages of EMU, which eventually led to the single currency, and set out the convergence criteria or economic tests that member states have to pass.
The treaty also introduced integration in employment and social issues - at least for some members.
The UK negotiated an opt-out of the so-called social chapter - a part of the treaty which was eventually adopted as a protocol and which covered issues such as workers' pay and health and safety.
Although, after a change of government, the UK did finally sign up to the social chapter, another aspect of Maastricht - subsidiarity - has remained a bugbear for Europe.
One of her friends, the Conservative MP, Sir Bill Cash, said he was "extremely sad".
"She really was a real trooper, she was tremendously loyal to us, she understood what was going on in that Maastricht Treaty.
"And she was completely determined to play a full role as a patriotic backbencher. And nothing would deter her. I don't think the whips had a slightest chance with her if I may say so.
"And the truth is that she was a wonderful fighter. And I'm really sad to hear about this."
Ms Gorman was one of the right-wing Maastricht Treaty rebels in the Conservative government, believing the treaty gave away too many powers to Europe.
She was a leading supporter of John Redwood in his leadership challenge to John Major in 1995, but said none of the 1997 contenders for the Conservative leadership were worthy of being prime minister.
At the time she called William Hague "a prepubescent political marshmallow".
She first stood for Parliament in 1974 as an Anti-Heath Independent. She was a councillor for Westminster City Council from 1982 to 1986
