Why is it ridiculous?
Because it's outside both the sentencing guidelines and the law?
I'd imagine he will receive a hefty fine and a disqualification.
There is information on gov.uk about the penalties for speeding:
The amount you’re fined depends on what the speed limit was and how much over it you were driving. It’s usually a percentage of your weekly income, up to a maximum of £1,000 (£2,500 if you were driving on a motorway).
You could also be disqualified from driving or have your licence suspended.
For a custodial sentence you'd need to be guilty of more than just speeding in England. Scotland is different however.