The government has announced it is extending powers to deport asylum seekers found guilty of serious offences.

Home secretary David Blunkett set out the move to deport more asylum seekers who commit crimes in the UK on Monday.

While asylum seekers sentenced to two years or more can already be deported, the new powers covering over 100 offences will apply to criminals convicted of serious offences who receive a sentence of less than two years.

"While I would expect lengthy custodial sentences to be passed on those guilty of such serious offences, I want to ensure there is no loophole that means that those who get shorter sentences get off lightly," Blunkett said.

The new move covers terrorism, drug-related offences, and violent or sexual crimes.

"It is unacceptable that those seeking the protection of the UK should abuse our hospitality by committing serious crimes and undermining our communities," said home secretary David Blunkett.

"Only a small proportion of asylum seekers or refugees are involved in such crimes but we must deal firmly with those who do."

While crimes were committed by a small minority of asylum seekers, there was a "disproportionate effect" both on their victims and on community relations, he argued.

"We need a message to go out that we will welcome you into the UK if you have a genuine wish to contribute to the country and your own well being.

"But I am not prepared to welcome you if you are going to make other people's lives a misery."

The Conservatives gave the announcement a cautious welcome.

"This sounds sensible and it maybe a rare example of the government acting wisely in the interests of the British people," said shadow home affairs minister Humfrey Malins.

"However, I fear this is yet another flashy headline which means nothing. Criminals, when leaving prison, could evoke the Human Rights Act, passed by this government, if they could face persecution on return to their country of origin."

Immigration minister Beverley Hughes also announced on Monday that improvements to the Dublin Convention had come into force.

The move is aimed at speeding up the process for returning asylum seekers to EU countries where they have already lodged a claim for refugee status.

"These measures, which both fulfil commitments made during the passage of the NIA Act, reflect our determination to improve the asylum system at every stage," she said.

"While the key component in our strategy is to reduce the number of claims, which we are now successfully doing, Dublin II will also boost EU co-operation to deal with asylum shopping.

"Member states will now be required to respond to our requests for information in six weeks, when before there was no limit and progress could be slow."