Allegations of a security lapse at Heathrow are being investigated by airport chiefs, a spokesman has confirmed.

Four guards are reported to have been suspended after an official complaint from airline staff.

Staff say they saw passengers walk unchecked through a security post used by employees and passengers on domestic flights from Terminal One.

The allegations come as a report is expected to say that the UK is under-funded and ill-prepared for the threat of a terror attack.

'Secondary searching'

A spokesman for BAA Heathrow declined to comment on individual cases or to say whether staff had been suspended.

But she said "the allegations are being investigated" and that any member of staff who did not carry out duties in the "correct manner" would be disciplined.

The spokesman added: "These allegations relate to secondary searching at a boarding gate.

"All passengers and staff reaching this point will have already undergone security searching at a main search area."

According to the BAA Heathrow spokesman, security staff must complete an intense training programme, approved by the Department of Transport.

Even though airport security has been increased since the terror attacks on 11 September a report by MPs, due out on Wednesday, is expected to say the UK's security plans are too lax.

The report by the Defence Select Committee will conclude that key government bodies, including the Ministry of Defence police and the Home Office, are not working together to keep the country secure.