Originally Posted by DeathSlam

If this was money in your bank account. and you spent it knowing or suspecting you were not entitled to it, you would be required to repay the money and committing a crime under the Theft Act 1968. In fact the burden is the other way round, you have to prove you had a reasonable expectation that you were entitled to it (and that seldom holds up in court). So probably best not to make an extravagant F booking as I suspect the same may apply to points (does anyone know for sure?).

To be fair, if I notice someone has given me too much change in a shop I tell them rather than pocket the cash. I know there are some who think I'm a sucker because of this.