Tito worked for Nasa before entering business

He has paid an estimated $20m for the chance to become the first private citizen to travel to the space station.

Mr Tito, 60, is expected to spend three weeks training at the Gagarin Cosmonaut Training Centre near Moscow before leaving for Houston in the US.

But his hopes of enjoying the flight of a lifetime appeared under threat last week when he was admitted to hospital suffering from pneumonia - from which he has now recovered.

There also appears to be some confusion over which of the ISS regulatory bodies is required to give his space trip final approval.

'Lifeboat' mission

Mr Tito believes he requires only medical approval from Russian doctors, but according to the US space agency, Nasa, the trip requires their approval.

Mr Tito hopes to blast off in April

Following his training in Russia, Mr Tito is expected to travel to Nasa's Johnson Space Centre in Houston to continue his preparation work, accompanied by cosmonauts Talgat Musabayev and Yuri Baturin.

The three are planning to arrive at the ISS on 2 May. They will deliver a Soyuz spacecraft to act as a lifeboat should a crisis require the ISS residents to make an emergency return to Earth.

The first manned ISS mission began on 2 November, with the arrival of US astronaut William Shepherd and Russian cosmonauts Sergei Krikalev and Yury Gidzenko.

Mr Tito had previously hoped to visit the ageing Mir space station, but his plans were dashed when the cash-strapped Russian Government decided to destroy the platform.