The UK Border Force's chief has been suspended after an allegation staff were told to ease up on immigration checks.
Brodie Clark, who is one of the most senior figures at the UK Border Agency, is said to have instructed some staff to avoid checking details of some travellers against Home Office watch lists.
He is similarly said to have issued instructions to members of the Border Force that they were not to check some biometric passports travellers carried.
Last night the Home Office refused to say why Mr Clark has been taken off duties, but confirmed: "Head of UKBA Border Force Brodie Clark has been suspended." The action was taken on Thursday.
Two other members of the Border Force are also said to have been suspended after potentially thousands of travellers were able to pass into the UK without proper checks being made.
Home Secretary Theresa May is reported to have ordered an investigation to establish the scale of the missed checks.
Staff working at border controls have been under pressure in recent months to reduce queues.
Earlier this year border officials were given approval by ministers to pilot a system in which they could use their judgment to reduce the number of passengers whose details were examined, rather than ensure all non-EU passengers are checked. It is thought that Mr Clark could have authorised staff to go beyond the terms of the trial scheme by abandoning biometric checks on non-EU nationals and the verification of fingerprints of non-EU nationals.
Keith Vaz, a Labour MP, said: "These developments are extraordinary in that they involve such senior members of the UK Border Agency.
"Only a day after the publication of our report which concluded that the Border Agency continues to fail we have this remarkable news.
"We will question the Home Secretary about this on Tuesday when she comes before the Committee.
"If her answers do not satisfy us I am sure the Committee will want to conduct its own inquiry. The Border Police are supposed to keep people out, not let people in."