It would probably be extremely hard (or probably impossible) to PROVE criminal intent.
Firstly, the CPS would have to show that A intended to PERMANENTLY deprive B of property belonging to him. A could simply say that he was making some temporary arrangements, to the way things were run, while awaiting a settlement of a dispute with B.
Secondly, there's a statutory defence to a charge of theft:
"A person’s appropriation of property belonging to another is not to be regarded as dishonest . . . if he appropriates the property in the belief that he has in law the right to deprive the other of it, on behalf of himself or of a third person"
A could simply say that he genuinely believed that B owed him a great deal of money, and that he was simply taking what was owed to him. (As long he genuinely believed that he had the right to take the goods and money, even if that belief was ill-founded, he could not be convicted of theft for taking it).
Chris