I can't see why you couldn't use it as a business account if it has all of the features you want. It says that it 'may be suitable if you manage funds for a charity or club' but doesn't say that this is all it can be used for.
If branches aren't aware of this account, as harbourmaster mentions, then print off the Internet page showing the details and take it with you to a branch when opening the account. Mention to them that you are starting a business as a personal trainer and need an account to pay this money into this account and I can't see it being a problem.
As you are not going to be paying employees there isn't a need for a full-blown business account. You just need somewhere to put your income from your business to keep it separate from your personal money.