Dishonestly would be a key factor there. If you believe you have the legal right to do that, or you believe that the owner of the goods would have consented, then you have not acted dishonestly, and there is no theft. If you do so to as you believe that the owner would not accept cash, you have acted dishonestly and thus there is a theft.[1]
Note that Velumyl was an appeal on the grounds that the defendant did not intend to permanently deprive, thus the money being different was relevant as he permanently deprived the owner of that specific property. Had the defendant contented there was no dishonestly -- that he intended to return equivalent funds and believed that the company would consent -- the decision may well have been different.
Note that Velumyl was an appeal on the grounds that the defendant did not intend to permanently deprive, thus the money being different was relevant as he permanently deprived the owner of that specific property. Had the defendant contented there was no dishonestly -- that he intended to return equivalent funds and believed that the company would consent -- the decision may well have been different.
[1] Theft Act 1968 s.2(1) https://www.legislation.gov.uk/ukpga/1968/60/section/2