The Fireworks Act 2003
Fireworks Act 2003 (c. 22)
5 Prohibition of supply etc. of certain fireworks
(4) The descriptions of persons which may be specified in fireworks regulations by virtue of subsection (1) or (2) include in particular persons who do not satisfy any conditions which are specified in the regulations and relate to any of the matters mentioned in subsection (5).
(5) Those matters are—
(a) the satisfactory completion of a course, or courses, of training relating to fireworks and the means of proving the satisfactory completion of such a course or courses,
(b) proficiency or experience in the use of fireworks and the means of proving such proficiency or experience, and
(c) the possession of insurance cover against liability arising from the use of fireworks and the means of proving possession of such cover.
All that said, although the act makes provision for regulations to require insurance, the 2004 regs. don't.
However... (bear with me...)
"(a) any person who is employed by, or in business as, a professional organiser or operator of firework displays and who possesses the firework in question for the purposes of his employment or business;"
As an employer its a requirement to have EL insurance, and given the above I can't really see how you can be "in business as, a professional organiser or operator of firework displays" and not have 365 insurance. Whilst its not PL insurance, I'm sure 'fireworks' would be fairly specific on a EL policy.
Reckon it would need a test case to sort it out - wouldn't want to be the tester though...