Brown has sounded a powerful warning to executives

The pay of top public officials has become a new part of the electoral battleground.

Labour and Conservative frontbenchers are falling over each other in their attempts to sound tough on earnings packages above £150,000 a year. Publicity recently given to the subject by the Taxpayers Alliance has, without question, changed the political weather.

London government's top officials are among those highlighted in the Taxpayers Alliance research.

In recent years many of the capital's civil servants have seen sharp rises in their earnings. The number being paid more than £150,000 has also increased. There are several reasons for this upwards shift.

First, the blurring of the distinction between the private and public sectors has made it easier to justify private sector pay rates for public officials. Politicians from both major parties have wanted to import more expertise from the private sector into running Whitehall, the NHS and local government. Where companies would have paid applicants more than public bodies, higher salaries have been offered. Second, public sector bodies have been in competition with each other to get the best staff as they have sought to hit government-imposed targets and performance benchmarks. Recruitment consultancies work with public bodies to find the most talented managers. Pay appears to have been ratcheted up as organisations have tried to get the best people.

Third, the publicity given to very high pay and bonuses within the financial sector during the boom years probably created pressure for top public officials to "keep up" with their super-rich peers in similar positions. Earning £1million a year working for an organisation was no longer impossible.

In London, the previous mayor Ken Livingstone adopted a policy of purposefully setting pay high to attract the best talent, particularly at Transport for London, where Bob Kiley was paid in excess of £500,000 a year. Mr Kiley's earnings and bonus generated pressure for higher pay elsewhere within TfL and, almost certainly, beyond. Public officials in New York appear to be on lower rates for comparable jobs.

The prime minister has today sounded a powerful warning about any public sector executive pay above £150,000. The Tories agree with him. Public opinion is on the march. A crisis that started in the banks looks set to chop the earnings of public sector bosses.

* Tony Travers is director of the Greater London Group at the London School of Economics.