Was he stopped at the time or a camera? If he was stopped at the time then he’ll already have identified the driver and only has to worry about the speeding offence. If he was not stopped at the time then the hire company will have identified him as the driver (charging him an admin fee for the privilege – in the UK they cannot pay the fine on his behalf!) and passed his details to the police. He will then have received his own s172 request from the police which becomes bit more serious if he’s ignored that.
It might just disappear.
It might turn into a court case then disappear.
It might turn into a court case where he can agree to plead guilty to speeding if they drop the s172 (harder to do remotely)
It might turn into a court case then found guilty in absence (only likely in E&W, unless he pleads guilty). If the fine was then unpaid it could cause problems on arrival to the UK.
if its turned into a s172 case, the fines are hefty, if it goes to court in E&W they’ll add prosecution costs on top. So his gamble is:
1. Do nothing and he might get away with it (but he won’t know until 6 months after the offence – which for the s172 request is the 28 days time to respond – so typically 6-8 weeks after the speeding so Sept?).
2. Email (don’t just call – you want a record!) the people who sent the paperwork he has to see where it is in the system and how it can be dealt with easily. They almost certainly can’t take payment for a fixed penalty notice now if one was issued in Jan. I’m not sure if they can process non-UK license holders by fixed penalty anyway?