He joined Simmons & Simmons in 1979, qualifying as a solicitor in 1981, and became an Associate of the Chartered Institute of Taxation in 1983. He became a Freeman at the Worshipful Company of Grocers in 1980. According to The Guardian in April 2016, "Troup... built a career advising corporations on how to reduce their tax bills". From 1985 to 1995, Troup was a tax partner at Simmons & Simmons. He joined the Treasury as a special adviser to Chancellor of the Exchequer Kenneth Clarke and returned to Simmons & Simmons as its head of tax strategy after the 1997 general election. Shortly afterwards, Troup wrote a series of Personal View commentaries for the Financial Times, including one titled "Double trouble over tax" on the problems caused because the UK has two separate tax authorities, the Inland Revenue and HM Customs & Excise, and the advantages of merging them. Another piece, Right result, wrong reasons, considering the reasons to abolishing tax credits on dividends. Why the chancellor is missing the point, on the flaws in the tax system and the importance of the rule of law in taxation, in which he expressed the opinion that "tax avoidance is not a moral issue" and described tax itself as "legalised extortion". Troup's article of 15 July 1997 was criticized by Richard Murphy of the Tax Justice Network in 2013. Appearing before the Treasury Select Committee on the subject of tax havens in 1999, as the Organisation for Economic Co-operation and Development began to take measures with regards to offshore companies, Troup immediately had to declare an interest with regards to the Code of Conduct, saying: "In relation to the offshore jurisdictions, assisting them putting their representations to the OECD". Asked if tax havens "mobilise capital which would not otherwise get itself mobilised and so increase international economic activity", Troup replied that "If it did not assist people would not pay for the use of those jurisdictions and those centres. My intuitive response must be yes, it does assist tremendously... It is difficult to see the world without many of these jurisdictions", adding "it is very difficult for UK residents or companies actually to reduce their tax bill legitimately through any offshore means". Troup advised on the management buyout of part of hedge fundMan Group in 2000, commenting that "achieving a tax-efficient structure in the context of a buyout involving businesses and shareholders round the world posed some interesting challenges". The new business owners of the company ended up holding their shares through a trust company in Jersey. Documents included in the Panama Papers leak demonstrated that Simmons & Simmons dealt with the Panama law firm Mossack Fonseca, at the centre of an international scandal on tax havens, tax avoidance and corruption. Papers obtained by the Süddeutsche Zeitung and the International Consortium of Investigative Journalists also reveal Simmons & Simmons' close relationship with running offshore companies and major overseas property owners, including an investment companyrun on behalf of Sheikh Hamad bin Abdullah Al Thani, while Troup was a tax partner.
Civil servant
Troup returned to HM Treasury in 2004 as Director of Business and Indirect Tax, and became Director General of Tax and Welfare at HM Treasury in 2010. In March 2016, Private Eye characterized Troup time in the Treasury as including a series of relaxations to laws regarding multinational corporations and alleged tax havens. He succeeded David Hartnett as the Tax Assurance Commissioner and Second Permanent Secretary at HMRC in September 2012. The last months of Hartnett's career were tainted with allegations of "sweetheart deals" involving Vodafone and Goldman Sachs. Troup was appointed as Executive Chair and First Permanent Secretary at HMRC from April 2016. It was announced in September 2017 that Troup would retire from HMRC at the end of the year. Troup was appointed a Knight Bachelor in the 2018 New Year Honours for "public service to taxpayers and the tax system".
