IIRC, modern doctrine puts an Army at anywhere between 60-100,000 personnel. Just as well there is a bit of flex these days otherwise the British Army would theoretically become a Corps in terms of pure numbers.
I suspect that might be somewhat politically embarrassing though and might be frowned on by CGS. If nothing else, they'd have to re-do all their advertising and stationery to reflect the changes! And can you imagine trying to recruit for the British Corps? Sounds like some sort of 1930s Mosley-esque organisation!