Tory MP Sir Geoffrey Cox faced criticism when it was revealed that he earned hundreds of thousands of pounds defending a tax haven in a corruption case brought by the UK Government. It came after the Owen Paterson affair thrust parliamentary “sleaze” into the spotlight, and it has also highlighted the issue of second jobs.

Sir Geoffrey started a new job on 1 November, earning £400,000 for 41 hours of work a month as a consultant for Withers LLP law firm, the latest Commons register of interests revealed. The arrangement is within the rules but has left many questioning whether he can devote enough time to his role as an MP. It has also since emerged that Sir Geoffrey earned more than £1m in the past 12 months working as a lawyer for clients including the British Virgin Islands (BVI), helping defend the tax haven in a corruption case brought by the UK Government.

The Rules

Ministers are not allowed to work second jobs, but all other MPs can. Over the last year more than 200 MPs made money on top of their MP’s salaries doing additional work. MPs must publicly declare all their additional earnings under the Register of Interests. They must also declare all gifts, donations and shareholdings over 15 per cent. After leaving their role as an MP, they must consult with the Advisory Committee on Business Appointments about any jobs they wish to take on over the next two years. They are also banned from lobbying the Government for this period of time. It is against lobbying rules for MPs to use their parliamentary power to benefit external businesses for which they work, so as to avoid any conflicts of interest.

This is what Mr Paterson was guilty of doing. The Parliamentary Standards Commissioner found he broke lobbying rules by approaching the Food Standards Agency on behalf of Randox and Lynn’s Country Foods – companies he was employed by – multiple times, and failing to declare his personal interests in communications.

Isabel Hardman, author of Why We Get the Wrong Politicians, argues that the “richness” argument does not hold because two classes of MPs exist: “Those in comfortable safe seats who have spare time for second jobs, versus those who represent marginals, spend their lives on the stump and incur much greater costs”. Many of these second jobs, she says, “are well-paid directorships helping companies navigate parliament”. The debate raises a deeper question about what it is to be an MP. Is it still a part-time public service role, to represent voters on top of a day job? Or is it a full-time occupation: legislator, social worker and community champion? If it’s the latter, it may be time to accept that the UK now has a professional political class, curtail most outside interests and duly up MP salaries, which lag behind comparable professions such as solicitors.

In 1995 the Committee on Standards in Public Life (CSPL), chaired by Lord Nolan, affirmed: "A Parliament composed entirely of full-time professional politicians would not serve the best interests of democracy. The House needs if possible to contain Members with a wide range of current experience which can contribute to its expertise."

Only a generation ago, most MPs expected to have another job at least part of the time. Until the reform of sitting hours in the 1990s, the Commons began work each day at 2.30pm, a schedule enabling many to continue with their profession at the Bar, or as a solicitor or journalist or doctor.

From the 1980s, another employment opportunity became widespread: acting as a consultant to a lobbying company or PR firm, in explaining parliamentary procedure and investigating the likelihood of legislation being passed.

A Guardian analysis of the Register of Members' Interests found that only 26 MPs declared more earnings from directorships, paid employment or shareholdings than they did from their parliamentary salary. Of these, 20 declared more than £100,000 in outside earnings.

A Telegraph analysis of the remunerated earnings part of the Register during 2014 concluded that of the 281 MPs who registered extra earnings, around 180 could be classed as having at least a second job.

Conservatives earned much more than Labour from these external interests. Of those 180 MPs with additional jobs, 112 – or nearly two thirds – were Conservatives. Forty-three were Labour MPs and 15 Liberal Democrats. Similar party differences are likely in the 2015 Parliament.

SNP MPs are not allowed to be company directors or to hold second jobs.