[danielf]

Originally Posted by TheDon

Luckily the theft act clarifies it to say:

So that is still theft as you taking it for 25 years is clearly a period equivalent to the outright taking. If you only took it for a short period that doesn't breach the others rights over it, it's not theft.

For instance, if you left your car unlocked with the keys in the ignition (so as I don't have to break into it) and I found your car and whilst you're asleep I drove your car around and then returned it (with any fuel I used replaced) that's not theft. However if I didn't return it before you woke up and needed to go to work, that is theft, even if I retuned it the same day as I breached your right to use it as you wished.

Credit where it's due. Good answer!