In 1996 John Major’s Conservative Government was hanging on by a thread. The handling of the Scott Report, which found that Government ministers had deliberately misled Parliament over arms sales to Iraq, had caused several defections, cutting the Government’s majority to three. Peter Thurnham, MP for Bolton North East and a party whip, took this as his moment to leave the party. Rejecting Major’s pleas for him to stay, Thurnham showed that minor MPs could, under certain circumstances, hold the Government to account. He later switched allegiance to the Liberal Democrats.

Some suggested that Thurnham’s resignation had less to do with Iraq than with his not being selected as the Conservative candidate for the Westmoreland constituency when boundary changes made his seat untenable. This failure was perhaps not a surprise, as Thurnham did not unfailingly toe the party line.

He entered Parliament in 1983, having won the extremely marginal seat of Bolton North East, which he also hung on to in 1987 and 1992. A great believer in the free market, he once declared that Britain would be better with one sweatshop than three million unemployed.

He was also a particularly keen proponent of embryo research. He and his wife, Sarah, had adopted a severely mentally and physically handicapped child, which threw him naturally into backbench issues on children and disability. When Enoch Powell introduced his Protection of the Unborn Child Bill, Thurnham campaigned against it. He formed strong cross-party alliances with Dafydd Wigley, of Plaid Cymru and others; heated debates resulted, leading on one occasion to the breaking of the arm of the Speaker’s chair. Thurnham spoke for more than three hours in a midnight debate using notes prepared by Robert Winston, the prominent fertility expert, on the correct procedure for sterilising test tubes.

He was a founder member of Progress, a campaign group of MPs and researchers that is now a charity promoting the benefits of IVF. Thurnham worked closely with Lady Warnock, writing two pamphlets that were influential in bringing majority backbench opinion behind Kenneth Clarke’s 1987 Human Fertility and Embryology Bill, which cemented Britain’s leading position in the ethics and legislation of IVF research. He also campaigned to make it easier to adopt children from abroad.

In 1987 Thurnham became parliamentary private secretary (PPS) to Norman Fowler at the Department of Employment, and then briefly to Eric Forth and Robert Jackson. From 1992 to 1994 he was the PPS at the Department of the Environment to Michael Howard, a contemporary from his days at university. During this time he sat on numerous committees, which included employment, public accounts and, as chairman, the smaller business committee. In Bolton he campaigned to improve housing in the more deprived areas of the town.

Peter Giles Thurnham was born in 1938 and spent his early childhood in southern India while his father, a tea planter, was away fighting in Burma for most of the time. He came to England aged 6 to be educated, eventually entering Oundle School. From there he won a scholarship to read engineering at Peterhouse, Cambridge. He went on to Cranfield Institute of Technology to take an advanced diploma in engineering, and then to Harvard University, from which he graduated with an MBA in 1969.

Thurnham’s first job was as a design engineer at NEI Parsons and then as a director of British Steam Specialties. He was married in 1963 and moved to Leicester where he and his wife started their own refrigeration and air-conditioning company, building it up to become the Wathes group of companies (later WR Group Holdings). The company enjoyed phenomenal growth and was listed in The Sunday Times Top 100 Fastest-Growing Companies for three years running. While in Parliament he gradually handed over control of the company to his wife, and on leaving Westminster in 1997 they agreed to split control of the company. Their marriage was dissolved in 2004.

Thurnham decided to sell up, retiring to a grouse moor on the Yorkshire-Lancashire border with his partner, Carole Emery, whom he married on May 9, only hours before his death. In his latter years he enjoyed vintage sports car trialling, culminating in winning the Lakeland Trial last autumn.

Thurnham was a patron of Stork, the Association of Families who have Adopted from Abroad, and vice-president of a local care home.

He is survived by his second wife and his two sons and three daughters.

Peter Thurnham, Conservative MP for Bolton North East, 1983-1997, was born on August 21, 1938. He died of pancreatic cancer on May 10, 2008, aged 69