For the benefit of the OP and other readers.
Firstly pay close attention to Hoggums post above, he is absolutely right in this degree and one could find themselves in trouble (or at least a huge tax bill if your lucky enough to make profit) should they not adhere to the law.
However:
Don't lose site of wording, that's crucial here as with any law or/and terminology. If in any doubt whatsoever see a lawyer who knows contract law and will point you in the right direction. DO NOT TAKE THIS POST AS ANY KIND OF ADVICE. Its just somewhere to start from.
Firstly, there should be no mention of trading - YOU ARE NOT - you are gambling, straight forward and simple. It works exactly the same as if you give me £10 or £1,000 to go to the bookies and place money on a horse, if it wins I collect and give to you, if it loses, tough.
Also, lose the word - PROFIT. You are not making profits if you win, see above, you are winning by gambling, not buying or selling a product or service - remember you are not trading - with your money or anyone else's.
Lose the word FUND and anything else related to this wording, you are not. You are also not providing a service or charging for a service. You are simply taking someone's money and gambling with it with their permission. If anything you are more of a consortium. For this you can have legally binding contracts drawn up with or without obligations.
If you stick to the above, then you are not a business nor a company. You are not guaranteeing returns or profits but simply gambling someone's money on their say so to hopefully win.
If on the other hand you wish to become a managed fund then you have a very long way to go, to be blunt you wouldn't be asking these questions on a bulletin board but would instead be sat in front of someone professional who's charging you many hundreds per hour.
Regards,
Lee Shepherd