It should already be illegal.
They are supplying alcohol to be consumed onsite and thus require a personal licence (Licensing Act 2003).
Section 111 ss.1(b) states
Personal licence means a licence which authorises that individual to supply alcohol, or authorises the supply of alcohol (1(b))
ss.2 states that the reference to an individual supplying alcohol is to him -
supplying alcohol by or on behalf of a club to, or to the order of, a member of the club.
(ss.2(b))
This essentially means that anyone who is supplying alcohol to a member (the punter) of the place requires a licence. So yes, it's illegal for a shotgirl to supply booze without a licence.
If the clubs main 'event' is the displaying of Morris Dancing, then you can serve alcohol without a licence! (Licensing Act 2003, Schedule 1, S.11)