Aside from minimum wage - it is up to settings to set their pay and whether they grade practitioners for their scale, their longevity and experience, or the duties they carry out in their role.
It becomes very complicated for managers to give everyone sliding pay scales when you may have an NVQ 4 with 4 years experience who comes into work and goes home with no added 'duties' or work and another NVQ 4 who has worked 12 years who untakes much more - and is willing to take work home as well as prepare things when the setting is closed. I pay by experience , but also by what their input is. The option is open to all, to maintain fairness, but there will always be staff who are very good - and choose to be so just for their contracted hours.
I do feel if your setting can afford it, they should increase the rates of pay you have printed - my deputy earns £12 an hour - worth every penny, newer staff start at £7 an hour - regardless of qualifications - when I employ good staff I want to keep them.
Even if your staff are only given a nominal annual pay increase of £0.30 -50p a session - it keeps morale up, and shows that staff are appreciated. I am also registered as a charity - but it doesn't mean you can't impove your revenue and reward your staff. If your setting's finances are transparent (you are allowed to look at them, if you are not shown, go on the charity website, put your charity reg no. in and you can look at the setting's annual accounts) and you can see if your setting can afford a little more ( someone needs to understand the feasibility of sustaining pay, and projecting/forecasting costs though) write down everyone's duties and suggest that you think staff should be recompensed by way of a £0.50p increase annually. If you are increasing you fees annually, there should be no reason why you can't increase your pay at least every two years, an if you can't afford it, you'd all understand.
Ultimately we all work to earn a living - hopefully we all choose to go into this sector because we enjoy the children and working with them, but people should be rewarded and not taken advantage of - if finances permit.
I think Nursery and Playgroup/Pre-school settings look at pay differently - a full daycare nursery will have different costs and may have many more staff to pay up for, they may have cooks, caretakers, cleaners etc. Therefore there will be more to pay out from the pot - something else to consider.