Security systems at Gatwick may not be tight enough to keep out terrorist attackers, despite a step-up in checks.

Undercover investigators have been able to walk on to planes with potentially dangerous weapons concealed in their pockets and hand luggage.

The breaches occurred despite a ban on carrying sharp objects announced in the wake of the September 11 terrorist attacks in America.

In one case, a reporter smuggled a miniature cleaver, a 3in stiletto knife and a 4in dagger on to a British Airways flight from Gatwick's North Terminal to Manchester.

The knives were not detected by the airport's security staff despite being passed through an X-ray machine.

BAA Gatwick spokesman Richard Stocks said: "Safety and security are of paramount importance and a full investigation into this alleged incident is already under way.

"BAA is committed to maintaining the highest levels of safety and security at all its airports."

Two Gatwick security guards who allegedly allowed another reporter to carry a multi-blade DIY tool, a 12in knitting needle and a sharp metal file on board a long-haul flight to Miami in November face disciplinary action.

All three objects were said to pass two of the heightened security checks introduced in response to the September 11 suicide hijacks.

The bag containing all three objects was checked by a second guard at the boarding gate but he failed to spot any of them. Both men are to appear before a disciplinary tribunal.

Charges against a 21-year-old builder arrested after two large fixed-blade knifes were allegedly found in his luggage when he flew in to Gatwick from America have been dropped.

Ben Harrington, of Reigate, Surrey, denied possessing an offensive weapon. Crawley magistrates dropped the charge on Friday, citing lack of evidence.

British Airways is thought to have ditched plans for a full-scale withdrawal from Gatwick, one option being considered in a report due to be presented at the end of the month.

However, under-performing flights to destinations such as Lyons, Naples, Bologna, Hamburg, Venice and Stuttgart and long-haul services to South America are likely to be cut.