However, if they do subsequently get a warrant and enter the premises, there is no way of knowing if they, as in some other agency, did not plant any data "via the back door".
Who knows all the files on one's hard drive. A hidden file (very easy to do) can lurk on one's disk for months and then be 'discovered' by the Authorities. They can create supposedly old files and sneak them on at any time, giving the impression that the file has been around for ages.
One group could plant the evidence and then tip off the regular Plod who just come in, take away the machines and discover all manner of material. As with the hapless chaps in Forest Gate, false, presumptive and self-serving leaks and rumours* can get out surprisingly fast - guilty until proven innocent.
Warrants were created for a very good reason. EUdenrats, Federasts and New Labour Lickspittles are clearly too arrogant and ignorant to realise how important they are. Forget the Boston Tea Party and taxation, the real unrest that spawned the American War of Independence was over the unwaranted (as in NO WARRANT) entry of private property by the King's Soldiers in search of documents not bearing the Stamp, and so the lack of the tax that goes with it. Sounds a bit like TV Licensing, if you ask me.
So, beware. A warrant is a vital part of property rights and thus Rule of Law. This has been tampered with. It is at their peril. They know not what they are doing, but think they do. Regardless, ignorance is no defence.
* they were "accused" of possessing child pr0n. It would be very easy to miss the retractions and corrections that dribbled out later, but by that time their names would be mud.