The rules, due to be introduced in April 2006, will allow people to include buy-to-let investment property in their pension pot.

As a result, many investors will be in line to claim pension tax relief.

Datamonitor said the change would mean that top-bracket 40% income tax payers would get relief totalling £2bn a year.

This is a tax break for the rich funded by all taxpayers - Julian Crooks, Financial Planning Service

The planned pension reforms will affect the whole market, but Datamonitor said that the option to claim tax relief on a buy-to-let property would prove particularly attractive to the rich.

Prohibitive costs

Datamonitor estimated that the vast majority of people taking advantage of the pension shake-up will be earning more than £75,000 a year.

The group said this was because the costs of setting up a self-invested personal pension, the necessary pension framework for claiming tax relief on buy-to-let property, were high.

"The government has underestimated the impact that the changes will make," said Oliver Guirdham, author of the Datamonitor report. "This constitutes a £2bn tax relief for Britain's wealthiest customers."

Julian Crooks, an independent financial adviser with the Sheffield-based Financial Planning Service, branded the buy-to-let tax break as a "retrograde step."

"This is a tax break for the rich funded by all taxpayers. The money would be better spent encouraging people on average incomes to save more for their retirement," Mr Crooks said.