@TheVogon "When you pick it up, it becomes a stolen hammer..."
No, which is why shoplifters don't get arrested in the store. The Theft Act 1968 states that a person is guilty of theft if they dishonestly appropriate property belonging to another with the intention to permanently deprive the other of it. It's that intent to permanently deprive that is important. This is also why there is an offence relating to motor vehicles of "Taking Without the Owner's Consent" (TWOC) because "borrowing" a car and intending to return it later is not theft.
There are some interesting wrinkles such as if someone takes money and then repays the exact amount they took they are still guilty of theft unless the money they put back is the exact same notes and coins as the ones they took.