'Hail requires vigorous convection, rather than deep'
Not sure what you mean by deep here.
At what height does it need to be before it can be called deep?
The Valentia tephigram here shows Cb tops possible to 400 hPA or about 22000ft.
There are plenty of them in view atm from Wembury giving rain mixed with hail showers. Temp 4C, dew 0C.
Had a sprinkling of snow at 0600 GMT when temp was 1C.
Len
Wembury
SW Devon coast