How is it that the police can destroy evidence?

Ricky Tomlinson holding a copy of Northern Voices at a Conference of the FBU

YESTERDAY, Brian Reade wrote a piece in the Daily Mirror about Ricky Tomlinson's claim that Richard Whiteley was a spy for MI5.  We produce an excerp below:
'Not convinced? Neither is veteran Shrewsbury 24 researcher, Eileen Turnbull, who believes Tomlinson may have been duped: “I don’t know why Ricky is saying this,” she said.
Well, having recently spoken at length with Ricky, I think I know why. The 77-year-old realises he hasn’t got too many fighting years left, and the lack of a pardon for him and his fellow strikers in the face of overwhelming evidence that they were framed, could be driving him to distraction.
In 1973, Ricky was jailed for two years at Shrewsbury Crown Court, and 23 others convicted, after being found guilty of arcane public order offences during a national building strike against poor pay and Victorian working conditions.
For 44 years, campaigners have insisted the convictions were instigated by Ted Heath’s Tory Government who feared the rise of trade union power.
They have documents suggesting police destroyed witness statements and framed testimony to convict the activists, and that crucial papers are being withheld because they are too damaging and embarrassing to reveal.'
The Royle Family starhad said:
'... had he know of his alleged involvement in the plot when he appeared on Countdown he would have throttled him.'
It looks like Ricky is keen to get this issue of the Shrewsbury Pickets out into the public domain.