Prime Minister Gordon Brown ordered a review of recruitment to the NHS on Wednesday after the arrest of several doctors in connection with an alleged bomb plot this week. Brown, who was faced with attempted attacks in London and Glasgow just days after becoming prime minister last week, also pledged to expand an international "watch list" of potential terrorists and to expand background checks carried out on skilled migrant workers coming to Britain. He told parliament his government would also look to sign new agreements with other countries to step up cooperation against terrorism and allow Britain to deport suspects. Eight people have been arrested in connection with the attempted bombings, including one in Australia, and sources say all are doctors or have medical links. Two are Indians and the rest from the Middle East. Police believe they have arrested the main suspects in the al Qaeda-style bomb plot, sources close to the investigation said on Wednesday. Brown said he had asked new security minister Alan West "to conduct an immediate review as to what arrangements we must make in relation to recruitment to the NHS because of what we know has happened over the last few days." The alleged involvement of doctors has caused shock in Britain, where nearly 40 percent of registered doctors are foreign-trained. "We'll expand the watch list -- which is the cooperation right across the world from Europe to the Arab states -- of potential terrorists so that we list them in such a way that authorities of different countries can be warned," Brown said in his first appearance at weekly parliamentary questions. "We'll expand the background checks that are being done where there are highly skilled migrant workers coming into this country. Where people sponsor them we will ask them to give us their background checks," he said.