"He denies it"

Well he would, wouldn't he?

"There is no evidence for it"

It will be a networked computer. There will be an audit-trail which will carry evidence of the person whose account was logged-in at the time the material was downloaded. Are you claiming that this audit-trail doesn't exist? Where is your evidence?

"Except the claims....of ex-cops with a grudge"

Where is your evidence of this simply being a matter of them holding a 'grudge'? Do you know the gentlemen personally? Have you discussed their views with them?

"It was ten years ago"

Are you claiming that their is a Time-Limitation on government ministers' Gross Misconduct? Evidence that this is the case?