A minimum £10 is a good general rule which I generally adhere to but it isn't an inflexible rule.
e.g.
Lots of compact small houses together. (few van moves)
Flats in OAP complexes.
Fronts only.
Fortnightly
But ... if it's a local authority semi size then nowadays that minimum is about right and even more so if the job requires a van move and hose reel in and out all for itself.
Mind you I have sections of compact old stuff at £7.50/£8.50 for which I would now charge £10-£12 and which still pays over £30 ph over a day.
Just thought I'd re-post this as it is the most sensible answer on this thread! 
Sensible post!
Agreeing to having a £10 minimum which you generally adhere to and then giving plenty of examples as to why you charge less than that minimum!
Acknowledging you have compact work that needs to be priced higher by 25-30%.
I read into this post you don’t know or understand the reasons for having a minimum price, and you knowingly continue to clean windows that are under priced.
Still think it’s the most sensible answer?
Pretty much - first the bits in red - I accept I can improve this and will raise it when I feel I will gain more than I lose. To get to a £10 minimum requires less than a 25/30% increase and the £11/12 jobs raise the overall average. I see little point in losing some even if I can gain others at £12 if it means more van moves/time spent. Now let me explain the other examples mentioned in my original post in relation to my round.
Small compact houses - this is one estate of a mixture of fronts only and full houses when they are in. They have three windows and a door at the front and the same at the back. For the full house I charge £10. But if due to access issues I cannot do the backs then I charge £6.50 for the front only so therefore am charging over £1 per window on a full house and over £1.50 per window when fronts only.
This estate earns me (depending on whether the backs are done every time) between £200 and £300 and can be done in an agreeable amount of time.
All day and the van moves no more than 400 yards. I believe if I tried to charge the £10 minimum then I would have custies ask to change frequency, phone beforehand or not bother. I feel no need to put that to the test.
Flats in OAP complexes.
I clean 16/20 out of 25 OAP sheltered flats (depending if they've died, gone to hospital etc
) with the van in one position. One person collects as much as possible before the day and the stragglers I collect on the day. They have seven windows each including a door and I believe that the circumstances of this situation allow me to charge £7 per flat. It is typically slightly under a mornings work with collections and banter included and I am happy with it.
If I charged £10 then I believe I would lose some or be asked to change the frequency or the caretaker would undercut me.
Fronts only
I've partially covered this above but I have a run of semi's on a main road which get quite mucky from the traffic. I clean the fronts only one month and the backs every other time. I charge £7.50 for the front and £12.50 for the whole house. I accept Ewan I could charge a tenner for the front but as there are three other window cleaners on this stretch charging £5, £7 and £10 for the fronts (I have the lions share (My 12 houses to their 3, 1 and 1 respectively) I feel I could lose some of my custies.
Fortnightly (edited)
Just understandable for those who have large areas like this. You could just do the glass quickly on two in three visits.
I'm not the most ruthless businessman, Ewan and I accept I could tweak here and there and probably will over time ... but thank you for your input I am always willing to learn.