IT firms will find it harder to recruit from overseas after home secretary Alan Johnson announced that immigration rules are to become tougher.

From next year, all jobs must be advertised to British workers in Jobcentre Plus for four weeks - up from two - before companies can seek to employ staff from outside Europe.

The minimum salary that will allow an individual to qualify as a skilled worker and be eligible to work in the UK will also rise from £17,000 to £20,000.

And overseas workers wanting to transfer to the UK must have worked for their firm for at least a year rather than just the six months needed prior to the latest changes.

Johnson said the government had fully accepted the recommendations of the Migration Advisory Committee.

"These changes will ensure that businesses can recruit the skilled foreign workers that the economy needs, but not at the expense of British workers, nor as a cheaper alternative to investing in the skills of the existing workforce," he said.

The commission made 13 other recommendations that will be adopted to ensure that the points-based system does more to support UK workers.

The committee's report said that intra-company transfers - often popular with offshore outsourcing companies - should not lead to a right to permanent residence. It also recommended the government give consideration to whether the level of resource devoted to enforcement of intra-company transfers is sufficient and whether the degree of transparency could be increased.

Unions and employment groups in IT have been critical in the past of firms that use intra-company transfers to bring in offshore workers to fill roles that may previously have been occupied by local staff.