Simon Richards, who has died of a suspected heart attack aged 67, was not a politician in a conventional sense, but his role as a campaigner for the Conservative movement over several decades was significant – not least in setting the course for Brexit, well before the term existed.

He never held elected office, or showed ambitions in that direction. Though he was a staunch Conservative Party member his focus was not on party politics. While personally convivial, he avoided the limelight, preferring to sit at the back rather than be up on stage.

In 2006, a decade before the EU referendum, Richards co-founded Better Off Out (BOO) and served as its chief executive. At that stage, very few Conservative MPs were prepared to advocate withdrawal from the European Union, in public at least. Douglas Carswell, who later defected to UKIP, was one, and Daniel Hannan was among the select group of Conservative MEPs to sign up.

David Cameron, elected Conservative leader in 2005, had said that the Party was not to “bang on about Europe”, and while BOO was not quite a proscribed organisation, a clear signal went out from Conservative headquarters and the party whips that involvement in it was considered “unhelpful”. John Maples, deputy chairman with responsibility for candidate selection, indicated that the leadership would form “a dim view” of any candidate who signed the BOO pledge.

Yet gradually more signed up, boosted by an endorsement from Lord Tebbit. It was a cross-party campaign: Labour’s Austin Mitchell and the UKIP MEP Nigel Farage were backers.

But its significance was its work among Conservatives. David Nuttall became chairman of BOO soon after his election to Parliament in 2010, and the following year he tabled a Commons motion calling for a referendum on EU membership by 2013; 81 Conservative MPs voted for it despite a three-line whip to vote against. This huge rebellion prompted Cameron to promise a referendum in the subsequent Conservative manifesto, and in 2016 Britain left the EU.