What happens if you don’t pay a taxi fare?

My friend got in a taxi home last night with other people he didn’t know drunk. When he got home he realised everyone else had left without paying. He then tried to pay on his card but it got declined due to him putting the incorrect pin code in and the card got blocked.

He then proceeded to tell the taxi driver there was money in the house and then came back out with another card to try again. However the taxi driver had already left by then.

What are the potential punishments for this? He said he will pay the full amount as he is worried it can be taken further but as it was a black cab he doesn’t know who the taxi driver was.

As there were other people in the taxi that didn’t pay does this make things more complicated?

(England)

Edit: he is now asking whether he should let the police know about the situation as it could help his case if it’s being taken up further.