you could go to 11.50 ph and justify it by suppling toilet brushes

I would look at it like this, how much more money do you need each month from your existing customers?
say 150 quid
divide that 150 between your customers and see how much extra it works out per customer.
if like you say you got some who you do more for then give them a bigger share of the 150, and the ones you do less for vice versa. and then increase your price every year with a letter explaining that in order to remain in line with the rate of inflation you have to increase your prices by 3%