Members of one of Britain's most prolific gangs of people smugglers, who bribed officials at the Indian consulate in Birmingham, were jailed yesterday. The people traffickers are thought to have made up to £25m in 12 years by bringing in an estimated 3,000 illegal immigrants.

At least one of the people smuggled had links with a Sikh terrorist group and police believe other terrorists and their supporters are likely to have entered Britain.

Police discovered evidence that a diplomat from the Indian consulate general in Birmingham, where visas are issued, took bribes and held clandestine meetings with members of the gang, Harrow Crown Court was told. Police also found evidence of corruption by two other members of the consulate's staff. Ethio-pian officials were also bribed to provide entry stamps.

Most of the people entering Britain illegally were Indians from two areas of the Punjab, who paid up to £8,000 for false passports and to be smuggled through Ethiopia, Dubai, Portugal, Spain and Germany. They arrived in England by air or ferry. On average five people a week were being brought into Britain, according to the National Crime Squad, which headed the international investigation.

The gang leader was Sarwan Deo, 43, an Indian national who lived in Handsworth, Birmingham, and first arrived in Britain in the Eighties. He was jailed for seven and a half years after pleading guilty to conspiracy to smuggling illegal immigrants into the UK.

Passing sentence, Judge Dawn Freedman said evidence from a police listening device in Deo's car showed he "rejoiced in [his] ability to exploit corrupt officials".

Earlier the court had been told that Deo "enjoyed an unusual association" with officials at the Indian consulate general in Birmingham. Officers overheard him complaining that some staff were asking for too much money and, at one point, wondered aloud whether one of them should be "blackmailed" because of his greed, the court was told.

The staff accused of taking bribes had been posted elsewhere since the conspiracy was exposed.

The surveillance also uncovered the bribing of Ethiopian officials in return for passport entry stamps, which helped illegal immigrants to complete the last stage of their journey to the West.

"In addition to corrupting immigration officials in Ethiopia, the suspicion was that he had a corrupt relationship with an official - perhaps in the British embassy in Addis Ababa - who would issue UK visas for Indian passport holders," said John Bevan QC, for the prosecution.

Of the remaining gang members, Deo's brother Sucha, 44, of Chadwell Heath, east London, was jailed for three years; Povytar Rai, 35, of Ladywood, Birmingham, who used skills "learnt by watching a film on television" to alter and forge passports, received three and a half years; Deo's "trusted lieutenant" Jarnail Saini, 38, from Germany, five years; and Sohan Kalyan, 49, of Bedford, four years. All pleaded guilty to conspiracy to smuggling illegal immigrants into the UK between January 2001 and October last year.

The Foreign Office said the National Crime Squad did not request any action against three diplomats implicated in the smuggling ring.