The scheme is designed to make it easier for highly skilled, younger workers to enter the country.

But it will be harder for low-skilled, non-EU workers to head to Britain.

Clarke says the system will simplify immigration. But Conservative spokesman Damian Green thinks the government will struggle to make it work.

Like similar regimes in Australia and the US, points would be earned for factors such as qualifications, work experience and language skills.

A certain number of points would be needed to be considered for a work visa, awarded for aptitude, age, experience, and the level of need in each sector.

Highly skilled workers such as doctors, engineers and IT experts would get the most points under the system, due in place from mid-2007 at the earliest.

They will be the only group able to come to Britain without a job offer.

But skilled workers, like nurses, teachers and plumbers would be able to come to the UK if they can plug shortages in the workforce.

A person applying as a low-skilled worker would be granted entry to fill specific job vacancies for fixed periods, with guarantees that they will leave at the end of their stay.

Other applicants would include students and special sectors such as sports people and employees of international companies based in the UK, plus visiting workers - such as musicians or those on working holiday visas.

Low skilled workers, students and visitors would only be allowed entry if their home country has a formal agreement with Britain.

The points system was first announced in February last year, but Mr Clarke unveiled the details on Tuesday.

He said the new regime would simplify the movement of people into and out of Britain and replace 80 different routes into the country.