I am roughly your area, in essex, i charge £55 first hour, £35 ph plus vat afterwards for domestic customers no problem, £60 for two hours call out for a commercial chain of shops is incredibly cheap, i would be looking at least £120 for first hour and £60 ph after that at standard hours
what is the maximum distance youll have to travel to the furthest store?
is this a 24hrs service youll be providing?
how quickly are you expected to be on site from them calling you up?
this could balls up your day, if your in the middle of a day job at the time!
Imho
double those figures at least!
think of the worst case they could throw at you and consider how much you need to charge on that basis
also go vat registered too if your looking at taking on work in the commercial sector, i personally would be vat reg even if i only done domestic works