According to data analyzed by the Sunday Times' Philip Beresford, compiler of that paper's annual "rich list," there has been a notable increase in the numbers of wealthy people leaving the UK to live and work in the Channel Islands and the Isle of Man in the past year. Using figures obtained from Companies House, the UK's central companies registry, Beresford's research finds that more than 6,700 directors of British companies are now registered as living in Guernsey, Jersey or the Isle of Man – 500 more than at the same time last year. The British Virgin Islands has also become a significant beneficiary of the outflow of British businessmen, with 615 UK company directors now based in the Caribbean jurisdiction, 18% more than were registered there last year.

Francesca Lagerberg, Head of Tax at Grant Thornton, suggests that, combined with Chancellor Alistair Darling's determination to crack down hard on tax avoidance as well as tax evasion, it is not surprising that the steadily rising tax burden on the well off is causing many to consider their options, with some already having taken the decision to leave the country for more benevolent tax shores.

"In conjunction with the 50% tax rate, the 1% increase in National Insurance from 6 April 2011 and the removal of higher rate pension relief, those wealthy individuals who are internationally mobile are now likely to start booking their flights out of the UK," she notes. "If the aim is to frighten high earners then the government has succeeded."

Meanwhile, Guernsey-based Clydesdale Bank International believes that the outflow of the wealthy from the UK could become an exodus when the reality of the 50% tax rate is more widely understood.

On the face of it, the 50% tax will only apply to annual income of GBP150,000 or more (currently taxed at 40%). But Clydesdale warns that when taxable benefits such as company cars or employee loans are factored in, the 50% rate could affect taxpayers with a salary of GBP90,000.

“We have already started to see and hear of intermediaries as well as individuals looking to transfer capital to institutions, or work with structures here in Guernsey," said James Blower, managing director of Clydesdale Bank International. “The knowledge that people earning less than the GBP150,000 threshold may also be liable for the full 50% tax rate could lead to even further enquiries. It may ultimately also mean a wider range of earners doing business in Guernsey."

Income that will be subject to the 50% tax can come from various sources, such as salary, taxable profit from a trade, state or private pension, bank interest, share dividends, rental profit, and redundancy payments.

In an attempt to tighten the screws further on wealthy taxpayers, Darling also announced in last week's pre-budget report (PBR) plans to further restrict pension tax relief for those earning more than GBP150,000 per year. Under these proposals, pension contributions made by the employer will now count towards the definition of income for the purposes of the GBP150,000 threshold. Prior to the PBR announcement, someone earning up to GBP150,000 and receiving an employer’s pension contribution up to his full salary was not caught by the restrictions.

The Chancellor also introduced a floor such that anyone earning a salary under GBP130,000 before the inclusion of employer pension contributions will not have their relief restricted.

“This apparently technical change effectively halves the starting point for the restriction of tax relief on pension contributions," Nigel May, Tax Principal at MacIntyre Hudson observed. "Apart from the political attraction of soaking the rich, it is difficult to see the rationale for this further tightening of the net."

“Yet again through an apparently technical measure the Chancellor has reduced the definition of how much you need to earn to be worthy of Labour’s tax assault on the wealthy," he added.