£5 a metre is the norm........really 
Your average 3 bed semi has 18ft of gutter each side (front and back) - thats 4.5M a side
£5 p/m is a good price if your clearing and then cleaning the guttering out.
I've thought about charging more on what the job involves. My plan is to make a bracket for my mobile to attatch to the top of a pole and make a video of the condition of the gutters. Then i can see what work is involved and charge accordingly.
There would have to be a min charge though, which i think £50 would be a good starting price. Im also thinking of offering a gutter survey. For £10, the customer can get a video recording of the condition of there guttering and make a descision on the job. Should they wish to have the gutters cleared and cleaned, the £10 would knocked of the price of the job.
Cheap and easy way of gutter survey with the option of showing the customer. Wont take long either if you have a laptop to transfer the recording onto whilst your there.