Section 1 (1) of the Theft Act 1968 gives the basic definition of theft as:
"A person shall be guilty of theft if he dishonestly appropriates property belonging to another with the intention of permanently depriving the other of it."
However, from the details you have given, it sounds more likely that he may have committed burglary, as opposed to simple theft, given that you say that he apparently has taken property belonging to you from a warehouse belonging to a 3rd party.
Burglary is defined by S9 of the Theft Act 1968 as:
A person is guilty of burglary if he enters any building or part of a building as a trespasser with intent to steal, inflict grievous bodily harm (or raping any person therein, or do unlawful damage to the building or anything in it. S9(1)(a)
The crucial words re Burglary, as far as I can ascertain from your details, are "as a trespasser". Did he enter without 3rd party's knowledge/permission? That is something for you to consider. How did he get into the warehouse? Who owns that property?
There may be a theft, it may be burglary, or your suspect may have a defence in law that he was merely recovering part of the debt which he believes you owe him.
He clearly needs to be spoken to as does this 3rd party and whoever owns the warehouse / allowed your suspect to remove the camera.
Attend your local Police Station with as much detail as possible and they will be able to make a more informed judgement as the best way to proceed, since so many facts appear to be missing from your post.
Good luck.