If your changing 50 quid a hour (excluding initial call out charges) outside london then you are either aiming at a specific high end market position or just trying to rip of the customer IMHO (note this is an opinion), can you seriously tell me if you went to an old vulnerable lady and did a few hours to find and resolve a fault then you would hit her with a £100 charge just on Labour alone?
I would expect closer to half that figure in the Yorkshire area, it is competition that decides the average charge rate and unless you have sort after skills that most don't then to charge such rates will not be good in a business sense of attracting new custom and landing quotations, yes one can get away with it but that relies on either those customers that do not get other quotations and thus are ignorant to the going rate but this becomes a little bit questionable if one goes onto specifically targeting the vulnerable, like I said before, I have sort after skills in the industrial industry and have to turn a lot of work away such is the demand but even I know where my bread is buttered and know I would quickly loose my customer base if I tried charging them £50 an hour an normal rate.
I have seen it happen to others who got greedy where they made a good living for a few yrs then slowly work dried up, they probably believe the work is no longer out there as a whole but the fact is they had a poor business model and became a victim of their own success and greed.
I do expect some to disagree and I am fine with that but I like to provide a service that is good and rates that are realistic as this has ensured that my business model lasts and thus far I am in my 10th yrs of self employment with plenty on and lots in the pipework, I started out when the financial crash happened and it only the fact I had a good business model that I got through some tough early times.