Ultra-rich foreigners are flocking to Switzerland in increasing numbers to take advantage of controversial lump sum tax arrangements offered by many cantons, Swiss Radio International (SRI) reported on Tuesday.

The number of tax exiles in Switzerland reached 4,175 last year up from 2,394 in 2003, according to the report, citing a survey by consultancy group KPMG.

The Swiss policy of tax break has attracted critics both within and outside the country.

Earlier this year a spokesman for French Socialist presidential candidate Segolene Royal accused Switzerland of "banditry" after Johnny Hallyday, a French rock star, announced he would switch residency for tax purposes.

Hallyday will join a growing list of multi-millionaire celebrities and business leaders moving to Switzerland, including musicians Tina Turner and Phil Collins, former Formula One driver Michael Schumacher and Ikea founder Ingvar Kamprad.

After moving to Switzerland, Hallyday would only pay 300,000 Swiss francs (about 246,000 U.S. dollars) in taxes by special arrangement, SRI said.

In comparison, Swiss tennis ace Roger Federer has to pay 3 million Swiss francs (2.46 million U.S. dollars) -- despite he and Hallyday both earning around 10 million Swiss francs (about 8.3 million U.S. dollars).

Rich foreigners living in Switzerland avoid paying tax on their total wealth and usually contribute a lump sum based on five times the rental value of their Swiss property instead, according to the report.

Switzerland's center-left Social Democrat Party has been campaigning to bring a halt to the tax break practice for wealthy foreigners.

"We are against lump sum taxation because it is not just and is in breach of the constitution. According to the constitution all citizens should be treated equally and taxed according to their ability to pay," Social Democrat spokeswoman Claudine Godat told SRI.