A lot of company's DO NOT cover you for the glass being worked on, which is kinda vital 
Gleaming do.
I have public and employers liabilty with them, and I pay £350.00 per year.
£350! Axa - 2m cover across the entire policy including damage whilst working on glass £98 per year. Only difference is sole trader no employees.
And thats why its cheaper altho thats still a good price for what you get