Police can confirm that Mr English was spoken to as part of the investigation, and a statement was taken.We now know that English told them that Barclay had recordings. The legal standard for obtaining a search warrant is reasonable grounds to suspect that an offence has been committed and that evidence of that offence will be found. That standard appears to have been met simply by Bill English's statement to them. They'd certainly conclude that in any other case (and did in the case of Bradley Ambrose). So why didn't they do so here? I think the answer is obvious: because the police don't want to rock the boat or potentially endanger their funding. Faced with an allegation against the powerful, they grovelled to power rather than investigating it. As fucking usual. Neutral, impartial enforcers of the law they're not.
In relation to why search warrants were not obtained during the investigation, Police have previously stated that there was insufficient evidence to seek such warrants.
And now they're refusing to reopen the investigation because it is "closed". This is simply arbitrary, and again serves to ensure that those in power are effectively above the law.