MPS today called for people who sell knives disguised as household objects to be jailed after a Blackburn company sparked a major security alert at Heathrow Airport.

Mark Philip Hilliard, 40, and Linda Marie Hilton, 31, both of Sunnybower Road, Blackburn, run a company known as Spytech, which offered customers a selection of knives.

Police said some of the "stealth" weapons had been advertised as undetectable by normal screening methods.

The two appeared before Blackburn magistrates yesterday for a series of offences after a police investigation which began when weapons bought from the Spytech website were allegedly smuggled onto aeroplanes.

John Rushton, prosecuting, handed exhibits to the court of other weapons sold by the company, including a pen which contained a metal knife blade, a lipstick knife and a hair brush containing a blade in the head.

Now the pair have each been fined £500 with £50 costs after magistrates found them guilty of offences relating to the sale of weapons.

Blackburn magistrates heard that selling several of the items seized, described as disguised knives, had been outlawed just four months before the search.

And the district judge dealing with the case, Paul Firth, said he was sentencing Hilliard and Hilton on the basis they had been ignorant of the law rather than deliberately flouting it.

But East Lancashire MPs have hit out at the fine.

Hyndburn MP Greg Pope said: "This sentence seems totally inadequate. I really can't understand why selling deadly and concealed weapons in the Internet does not carry a custodial sentence."

In 2001 Heathrow police were contacted by airport security after an article appeared in a Sunday newspaper claiming the so-called 'stealth weapons' sold by Spytech were smuggled onto two flights.

Blackburn MP and Foreign Secretary Jack Straw promised an investigation, and police searches uncovered large stocks of the weapons hidden at Spytech's base in Blackburn ready for sale through the internet and mail order.

Mr Straw declined to comment on hearing of the fine, until he had seen all the details of the case, but Burnley MP Peter Pike said such offences warranted a prison sentence.

A spokesman for the Metropolitan Police, which covers Heathrow, said that in September 2002 Heathrow police received a complaint from the British Airport Authority against Spytech.

"Spytech advertised an assortment of knives and other offensive weapons that could be purchased by mail order. Some of these had been advertised as undetectable by normal screening methods."

Hilliard and Hilton each pleaded guilty to three charges of having their possession for the purpose of sale a disguised knife and three charges of selling knives suggesting their suitability for combat. Seven other offences against each defendant were withdrawn.

David Griffiths, defending, said the regulations relating to disguised knives was passed into the law in June 2002 in response to the September 11 terrorist outrage.

"Unfortunately very few people knew this had been added to the statute book," he said.

He produced items which he said also breached the disguised knives regulations which could be bought on the high street. "They are all making the same mistake as my clients," he said.