Normally pikies, and very nasty with it - watch out for the ones with no neck!
The taking of any sort of game (and hares are game,not vermin, like rabbits) is illegal on a Sunday, and so an offence.
Aggravated trespass (the max. offence Mon-Sat) is a civil offence, for which the police seem to do less than nothing.
Thames Valley in South Oxfordshire have had effective Sunday Farm Watch days, with a small team of officers pattrolling and responding. They made about 30 arrests last year, and picked up other offences along the way including unpaid fines, red diesel in cars etc.