GgW, sounds like you are running a decent outfit there, £30 an hour is quite fair.
A lot of places only pay £20/hr flat rate, and I know some that pay £15/hr and £10/hr for trial lessons.
The other problem is that some schools take on far too many instructors, as they are self employed and have no retainer, so when the school is busy they can maximise the use of the aircraft, but when it's quiet or the weather is particularly bad, the instructors are stuck.
I've known guys fly between 400 and 500 hours, so even at your £30 an hour it's only £12,000 - £15,000, and at £20 an hour it's really not enough to live on.