Despite assurances that he would slash his personal business commitments, Mr Hague has not only kept all his non-executive directorships and advisory posts, but added another position during the 15 months since Mr Cameron appointed him Shadow Foreign Secretary and de facto deputy party leader.

His portfolio of extra jobs now stands at five.

The Yorkshire Post can also reveal that the Richmond MP took time out from the 2005 General Election campaign to act as a paid speaker at five commercial functions, netting him more than £30,000.

They included two appearances in London with just a week to go to polling day.

At the time the former Tory leader was the party's cheerleader-in-chief for its target seats in the North, the Midlands and Wales.

The scale of Mr Hague's earnings provoked concern last night from Tories, although supporters praised him as a hard-working MP.

One prospective Parliamentary candidate for a Yorkshire seat at the next election – who asked not to be named – said: "William should be out there raising money for marginal seats, not himself.

"If he's got all this time to spare he needs to be out supporting candidates in the seats where we need him, even more so during a general election."

The latest edition of the register of MPs' interests shows that since his return to the political front line in December 2005, Mr Hague has starred at 27 functions and earned between £265,000 and £400,000 from them.

He had promised to re-channel his efforts into getting a Conservative government elected and pledged to reduce "drastically" his speaking engagements.

But Parliamentary records show that over the same period Mr Hague added a job with developers Dunalastair Ireland Ltd to non-executive directorships of a Rotherham engineering firm and a Dublin-based utilities company, plus posts advising a private equity firm run by an old Oxford friend and the JCB Group.

A trawl of earlier editions of the register also un-earthed the appearances – at events like the British Insurance Brokers' Association conference and Employee Benefits Awards – after Tony Blair fired the starting gun for the May 5 poll in 2005.

The Yorkshire Post invited Mr Hague to comment last night – but the party put up his deputy on the Northern Board, former Tory Minister Michael Bates, to reply on his behalf. "I see him as one of the most accessible and hard working members in the North," said Mr Bates.

"I just don't recognise the criticism. Anyone that knows his work rate knows that his party and const-ituency come first and these he gives great service to.

"He spends 95 per cent of his time working for the party. His income has fallen by two-thirds in terms of speaking engagements since he returned."