Can i assume that this is office cleaning?
If so, £10 per hour is way too low!
Do you employ staff?
If so, how on earth are you making a profit?
By the time you factor in wages, holiday pay, consumables, uniforms, training etc, etc. you cant be making much from this contract.
Clients will always try to keep your charges low, this is why, you should never ever let them convice you to charge for your services by the hour. The min wage is due to be increased again later on this year, which makes your current charges again look far too low.
My advice, would be to go back to the customer and explain, that you are properly insured, you are covered for product liability, key loss etc, arent you? The cost of your chemicals, materials, equipment etc, and that your prices reflect this.
I think that you may have to bite the bullet on this one, especially as this contract seems very important to you, but your increase is only an extra £7:50 per week.
Out of that increase, you must pay the min wage increase, allow for inflation etc!
Good luck!!!!
You must educate your client, perhaps it may be to late for this customer, but in future, you must explain that your charges reflect your real costs in offering your services, which are much more than just "the cleaning", insurance, training, equipment, maintenance of equipment, health & safety, admin, advertising etc etc.
My opinion, you are charging far too little for your services, regards Rob.