Unless it's a single seater under 910kg MAUW, it's technically illegal hire, but you can make it legal quite easily.
If you sell them each a 1/20th share at a nominal sum - say £1, and they contribute their fair share of operating costs, you're fine. To cover the realities of the situation, knock up a quick contract of sale that says they can only sell it back to you or your heirs and successors for the original sale price unless you agree otherwise in writing - and pretty much everybody is covered.
G