If you had a £10 min charge, you would get £30!!!
An example from my round would be when I had a call from a new customer the other day wanting me to clean 3 skylights on a monthly basis on his single story barn conversion. They are all next to each other and are only about 10inches wide by 18 inches long. I told him that I could fit him into the round but my minimum price is £10, thats fine he said, and he was delighted with the results from the first clean.
I'm not criticising you LWC, I just think it would benefit you and others to set a minimum price of at least £10