Under fire: Northamptonshire Police have been accused of helping cover up the Cyril Smith scandal

A police force was last night accused of helping to cover up the Cyril Smith scandal because of the involvement of the security services.

A Freedom of Information request was made for any details held by the force about an incident in the 1980s where the politician was stopped on the M1 and then arrested after child porn was found in the boot of his car.

But Northamptonshire Police say laws relating to the security services prevent the force from divulging any information it holds on Smith.

It cited Section 23 of the Freedom of Information Act, which concerns ‘information supplied by or concerning certain security bodies’.

Last night a victim and a campaigning MP condemned the decision as a ‘cover-up’ and called for the information to be released by the security services.

After 29-stone Smith died, it was revealed that he was a paedophile who repeatedly escaped police and court action despite sexually abusing boys for decades.

Labour MP Simon Danczuk said: ‘This confirms what we’ve always suspected: that the security services were involved in covering up the crimes of Cyril Smith and it is time for the authorities to reveal to what extent they were involved.

‘Failing to release these documents perpetuates the cover-up that has been going on for four decades.’

Kevin Griffiths, 66, who was abused by Smith in Rochdale, said: ‘This stinks to high heaven. Have lessons not been learnt that covering up these crimes is so wrong? The security services – MI5 – should release any files concerning Cyril Smith so the victims can finally have some closure on this.’

He said the fact the force is citing the security clause is clear proof of MI5 involvement.

‘It’s shocking to think we live in a society that protects paedophiles and abusers while the victims are refused any justice through the use of the secrecy laws,’ he said.

Smith, the Liberal MP for Rochdale, who died aged 82 in 2010, was allegedly stopped on the M1 in Northamptonshire during the 1980s on suspicion of a driving offence.

A search of his car unearthed a collection of child porn and he was arrested and taken to a police station to be questioned.

But it is understood he was released and allowed to leave after making a telephone call to an unidentified third party in London. According to Mr Danczuk, who also represents Rochdale, police received at least 144 complaints by victims about Smith but MI5 and Special Branch put pressure on officers to drop investigations.

After 29-stone Smith (pictured left) died, it was revealed that he was a paedophile who repeatedly escaped police and court action. Labour MP Simon Danczuk (right) has condemned Northamptonshire Police's decision not to release details on Smith's arrest in the 1980s because of the involvement of the security services

And he believes MI5 repeatedly stepped in to orchestrate a cover-up throughout Smith’s political career to protect other establishment figures from investigation.

The incident was described by Mr Danczuk in his book Smile for the Camera: The Double Life of Cyril Smith – which was serialised in the Daily Mail and blew the lid on Smith’s perverted past.

In March, Northamptonshire Police announced a cold case review of their dealings with the MP over the allegations made in the book. In response to the BBC’s FOI request, the force said it could ‘neither confirm nor deny that it holds any other information’ about the case.

It also cited other exemptions under the Act, including those relating to law enforcement, personal information and investigations.