Legally he shouldn't be driving until he's been clear for at least one year, as far as I know - unless a consultant thinks it's unlikely he's going to have a seizure again (which sounds like it wouldn't be the case, if he's had one/more (?) before this)
He really needs to see a doctor as soon as possible if he hasn't been diagnosed with an epilepsy or another seizure disorder - he ideally needs testing to find out what's going on (as seizures can be caused by all sorts including brain injury, brain disease, diabetes, medications, cardiac problems) and most likely a trial of medication if he's not already taking anything for seizures.
He shouldn't need medical attention today, unless you observe a decrease in consciousness/responsiveness or anything seizure like in which case you're best to call 111 or 999 (not necessary every time he has a fit, but if they're of unknown cause they always need medical attention asap).
That said - noone would think anything of it if you did consult NHS direct or such like for advice today.
However - he will need to contact his GP first thing tomorrow, whether or not you seek help today.
It's honestly imperative for your and his sake that he finds out what's happening.
I also wouldn't let him drive until he's seen a doctor, who will also most likely advise him not to drive for a while.
That all said - I'm not a doctor, I'm just writing from experience as DM suffers seizures.