Andy McSmith: Brown will be fuming over Tory letter-writing campaign

Nothing improves a politician's credibility more than having interested outsiders step in to help sell a controversial policy. The public is not much in the mood to take George Osborne's word that he can find the money he will need if he reverses Alistair Darling's proposed rise in national insurance just by cutting government waste.

But having the chief executives and chairmen of 23 large companies step forward and endorse what he has said makes Osborne's job much easier, and puts Labour in the uncomfortable position of arguing that people like Simon Wolfson, the chief executive of Next, are being taken for a ride by the Tories.

Actually, some – perhaps all – of the 23 know exactly what they are getting into by identifying themselves publicly with what they greatly hope will be the winning side. Some are in line for peerages if David Cameron becomes Prime Minister next month, according to a very well-placed source in the Conservative Party.

The 23 names included five major Tory party donors, who between them have given more than £500,000 either personally or through their companies. Lord Harris of Peckham, the boss of Carpetright, is a Tory peer and one of the party's biggest individual backers. He gave £250,000 to the Conservatives during the last three months of 2009. Another signatory was Sir Anthony Bamford, chairman of the construction equipment maker JCB, whose company is one of the party's biggest corporate backers. JCB donated £105,000 in the last quarter of 2009 and £130,000 the year before. In 2008, it also gave £75,000 to the now defunct Conservative Constituency Campaigning Services Board, while Sir Anthony has also personally given nearly £15,000 to two Conservative constituencies, including £9,999 to David Cameron's association in Witney, Oxfordshire.

Mr Wolfson is so well known as a Conservative supporter that it has been rumoured that he is in line for a ministerial job in a Cameron government – although he has said in public that he is happy to continue running Next. Mr Wolfson is listed six times on the records of the Electoral Commission as a Tory donor. One donation was for £4,000; the other amounts are not specified.

Another signatory, Sir Christopher Gent, the chairman of GlaxoSmithKline, is also listed as having donated to the Tories at least six times. Two of the donations came to £5,000. Aidan Heavey, the chief executive of Tullow Oil, is listed as having given £5,500.

Their intervention comes hot on the heels of a letter in The Sunday Times in February, signed by 20 economists, which said that the Conservatives were right to be thinking in terms of sharp cuts in public spending. It is followed by another today from seven groups representing business of different types, including the Confederation of British Industry.

This must be especially galling for Gordon Brown and Lord Mandelson, who were so successful in getting a parade of millionaires to turn out for Labour in 1997. They know how these things are organised and must be wondering: "Why them? Why not us?"