When Sir Bill Cash entered parliament, Rishi Sunak was just three years old. Four decades on, Cash is 83 and the oldest member of the House of Commons. He has become a deeply establishment figure and someone who has caused huge trouble for political leaders – from John Major, as one of the “bastards” during the Maastricht treaty era, to Theresa May during the battles over her EU withdrawal bill. Sunak is the latest victim of Cash’s so-called “star chamber” – a grandly titled group named after the unaccountable Stuart court of common law judges and privy councillors that met in Westminster until its abolition in 1641. The original star chamber, a symbol of arbitrary and oppressive power, could impose any punishment short of death – from whipping to the excision of ears. The modern incarnation of the group is less terrifying: it is merely a self-appointed group of Eurosceptic lawyers, led by Cash, that publishes its legal opinion. But it is still capable of striking fear into the heart of prime ministers – such as with its verdict on Monday that Sunak’s Rwanda bill was not sufficiently “watertight” against challenges made on human rights grounds. A rump of Eurosceptic Conservative MPs set great store by the star chamber’s judgments. This will be the second time a prime minister has struggled with a parliamentary vote after MPs were swayed by its adverse opinion. In contrast, Boris Johnson received a boost when the group decided in favour of his new “oven-ready” Brexit agreement in December 2020. As its leading parliamentary expert, Cash’s style has never been flamboyantly headline-grabbing but rather assiduously legalistic. His method of undermining the centrist wing of the Tory party is through the publication of legal opinions and using parliamentary process to pick holes in the other side’s case. Cash was born during the second world war and his father died on D-day when he was four. He studied at Stonyhurst College, a Catholic private school in Lancashire, and then read history at Oxford University before qualifying as a lawyer in 1967, specialising in constitutional and administrative law. He entered parliament in 1984 for Stafford, and from 1997 the seat of Stone, and still runs a firm of solicitors from his home, called William Cash & Co. His parliamentary career has never involved a government job, but he spent several years as shadow attorney general under Iain Duncan Smith’s leadership of the Conservative party. As a backbencher during the Major and later the Cameron and May years, Cash had the opportunity to fight for his obsessive cause – Euroscepticism and, as he saw it, restoring sovereignty to the UK. He built up knowledge of Brussels while spending more than 30 years as a member and now chair of parliament’s European scrutiny committee – once describing the decision to put him on the group as “the worst mistake the whips ever made”. Over that time, he has shifted from having a reputation as someone on the anti-EU fringes of the party to someone whose opinion is held in high esteem by the pro-Brexit right of the Conservatives. The closest he has come to major controversy was during the MPs’ expenses scandal when it was found he was claiming from the taxpayer to rent a room in Westminster from his daughter, when he already owned a property not far away that was occupied by his son. It was found to be within the rules, but the public outrage was so great that he agreed to pay back the £15,000 paid to his daughter from the public purse. Colleagues regard him as courteous but one former adviser said he was “rather tedious” and prone to relentlessly “banging on about Europe” – as Cameron once urged his party not to do. Outside parliament, Cash devoted time to restoring an Elizabethan moated manor house in Shropshire where his son, William Cash Jr, a journalist and former Ukip spokesman, now lives. Cash himself lives in a converted barn on the estate with his wife, Biddy. Having said he will stand down as an MP at the next election, Cash will no longer make lengthy interventions on procedural points or laying forensically worded amendments. But it is hard to imagine him ever keeping his counsel on the subject of British sovereignty and Europe.