The Driving Licence on its own is not really of any use in the circumstances I mentioned above. Yes, a licence is perfectly acceptable for check-in purposes as you say, but that was not the point of my post.

If the OP's friend is airside and his biometrics somehow fall out of the system, because he will have mingled with passengers who have not cleared the UK border, he may need to establish his right to be in the UK. If a driving licence indicated the holder was born in the UK/EU it is no problem, but the OP's friend as a visa national his licence (if he has one) will show he was born in another country.

We are told there is no passport available, so to avoid a possible delay in making his flight (in the very unlikely event his biometrics fall off of the system) he may be required to establish by other means his identity and his right to enter/remain in the UK.