Tax relief on pensions for employees with an income of £150,000 or more will be tapered downwards, falling to 20% for those earning more than £180,000 as a result of the Finance Act 2009, which has received Royal Assent.

The Act also contains anti-forestalling measures designed to prevent high earners from making large additional pension contributions before April 2011, when the new rules become effective.

During the passage of the legislation through parliament, concerns were raised that there was no provision to protect contributions to defined contribution (DC) schemes made less frequently than on a quarterly basis.

This issue has been addressed by an amendment in the Act stating that for contributions made less often than quarterly over the past three years, the special annual allowance will be increased from £20,000 to the average of those contributions, but capped at £30,000.

According to law firm CMS Cameron Mckenna, the amendment will assist high earners who are self-employed or who, in practice, make annual, often variable, contributions.

Helen Dowsey from Aon Consulting, however, believes that the changes outlined in the Act are hastening the demise of final salary schemes.

She said: “The changes announced by the Government in the recent Finance Act which received Royal Assent yesterday, represent another nail in the coffin of pensions tax simplification and could hasten the demise of the final salary scheme in the private sector.

"Much of the detail post-2011 has still to be announced, but the Anti Forestalling measures included in the Act, which will see us through to 2011, make it clear that future pension provision for high earners is fraught with danger and many may be turned off.

"Whilst post-2011 detail is scarce, what is clear is that High Earners should be seeking financial advice. Employers with such staff should be communicating the issues to them as well as giving serious consideration to the shape and structure of their remuneration package going forward."

The proposals relating to tax relief on pensions outlined in the Finance Act 2009 were first announced in Chancellor Alistair Darling's Budget report in April.