John Hutton: foreign doctors make a huge contribution

But the Department of Health said it was for NHS trusts to ensure doctors had adequate English and a new system of annual appraisals should reveal any weaknesses in language.

Labour Health Minister John Hutton said foreign doctors made a huge contribution to the NHS.

"This attack by the Tories is a slur on the reputation of the vast majority of hard working staff in the NHS," Mr Hutton said.

The Tory party is getting nastier as it gets more desperate

Nick Harvey, Liberal Democrats

He accused Dr Fox of attacking overseas doctors "to hide from the public their real agenda which is about cutting �16bn pounds in public services and privatising the NHS".

"The Tories did not raise or address this issue in their 18 years in government," he added.

'Thinly-veiled racism'

Liberal Democrat health spokesman, Nick Harvey, accused Dr Fox of "thinly veiled racism" according to the Sunday Times.

"This is disgraceful, and a slap in the face for the many hardworking doctors who have come from abroad and given their all for the NHS," he reportedly said.

Nick Harvey MP says comments are racist

"First their attack on asylum seekers, and now this - the Tory party is getting nastier as it gets more desperate."

But Dr Fox denied the accusations and said the Tories were happy for the UK to accept trained doctors from anywhere in the world, as long as their English was good enough.

An increasing number of complaints are being upheld against doctors who were first registered overseas, according to the Conservatives.

Dr Fox said he believed inadequate knowledge of English is often to blame.

'Fatal'

He criticised the current English exam to assess foreign doctors in the NHS.

He is reported to have said it tests for only a "minimum" level of competence in English in the Sunday Times, and that this is not acceptable.

Dr Liam Fox: Poor knowledge of English can cause mistakes

"In potential life-and-death situations having a minimum standard of proficiency in English can be fatal," he reportedly said.

An estimated 25% of NHS doctors qualified overseas. Among junior doctors the proportion from abroad has risen to 38%.

No language test is required for doctors registered within the European Union.