1) It isn't irrelevant.
2) It wasn't provided as collateral. It was provided as proof of ID, and the driver held onto it without permission.
What? I said that whether an extra charge was reasonable or not was debatable. That's nothing to do with if the driver doesn't return the passport, which...
As others have said, it's not legitimate collateral, the taxi driver is not allowed to keep it, it belongs to the government.
That's debatable, and if fair then so is the removal of the payment for the inconvenience the OP has had by the driver not showing up.
If the original bill is paid and he...
At first your son inconvenienced the driver - now he's inconvenienced you. I wouldn't pay a penny more than £10. If he doesn't return the passport, I'd report him to the police for theft, he has no legal right to hold onto it.
Sorry I thought it was £15 total, not £15 on top of the £10?
Don't...