Britain risks being seen as a "safe haven for evil" by criminals responsible for genocide, war crimes and torture abroad, who effectively face no threat of prosecution here, lawmakers warned on Tuesday.

The government needs to close a series of legal loopholes which currently let criminals in with "impunity", reported The Times of India quoting chairman of the British parliament's joint committee on human rights, Andrew Dismore, who wrote the report.

Officials have investigated 1,863 people in Britain suspected of links to genocide, war crimes or crimes against humanity since 2004, campaign group The Aegis Trust told the committee.

"The government has chosen not to implement (international) conventions to the full extent possible, leaving inconsistencies and gaps in the law," the report said.

"These gaps effectively provide impunity to international criminals, allowing them to visit and in some cases stay in the UK without fear of prosecution."

Dismore added: "The UK must not be a safe haven for evil".

"The message to those who have perpetrated the most heinous crimes imaginable must be clear: they are not welcome here not to visit, not to live, not to holiday, shop, or get medical treatment."

The government should close the loopholes as well as steps like re-establishing a police war crimes unit to chase down criminals, the committee said.

A spokesman for Britain's Ministry of Justice said it was "committed" to tackling the kind of crimes outlined by the report.

"Although our strong preference is for those alleged to have committed such terrible crimes to be brought to justice in the place the crimes took place where this is not possible we must be able to use our own law against those who live here," the spokesman added.

Last month, ministers said they would extend a law allowing prosecution here of British nationals and residents for crimes committed anywhere in the world from 2001 to cover genocide, war crimes and crimes against humanity from 1991.