You can charge what you want the government dont care as long as they see you are passing there cut back which on flat rate is 10%
so dont pass it on to domestic custys and you lose by 10% or increase slightly
on commercial they expect the 20% vat anyway ...
Its not as bad as you think, most businesses manage with vat as they have too , window cleaners are usually fortunate enough to make a good living under its threshold due to a lack of significant overheads , i could work with one guy and profit about £35000 a year and not have to pay vat , but if you want to expand you must cross it simple as , or not be totally honest about cash but i doubt you wanna go down that road