Home Secretary Theresa May has been accused of a cover-up after she used legal powers to keep parts of a critical inspection into UK border controls secret.

Fifteen sections of the report into controls between France and the UK have been redacted - including part of a passage revealing staff and managers fear resources in Calais are stretched - for national security reasons.

Politicians and campaigners have accused Mrs May of hiding "her own failings" exposed in the report by chief inspector of borders and immigration John Vine.

Chris Bryant, shadow immigration minister, said: "This cover-up and the failure at our borders provide yet more dents in this Government's much-tarnished credibility."

In unredacted sections of the report, Mr Vine warns thousands of illegal immigrants attempting to sneak into the UK through France have not been fingerprinted by border officials for nearly four years.

The report reveals Border Force - the Home Office law enforcement wing stationed at ports and airports - is fining drivers and firms guilty of bringing in illegal immigrants at way below the maximum allowed by law.

Mr Vine reveals border staff remain concerned over the effect of the so-called Lille loophole, which effectively exempts some passengers who travel to Britain via Lille, in France, on Eurostar trains boarded in Brussels, Belgium, from UK Border Force immigration checks.

A Home Office spokesman said: "In accordance with the UK Borders Act 2007 the Home Secretary, in ­consultation with the independent chief inspector, is required to redact any ­material which, if published, would be prejudicial to the interests of national security."