How long are these warranties going to be for? 6years
What warrenty do customers get at present if they don't opt to purchase the insuranced backed warrenty? Bugger All
What do the insurance backed warrenties cover, that would not be covered as standard, or by the tradesman's Public Liability Insurance? Cost of rectification for non-compliant notifiable work.
If I were a customer, I would expect the work to comply with current Regulations, and for everything to work correctly for at least a year.
If you then consider the life expectancy of cables and accessories, and the fact that guidance indicates that domestic installations should be inspected every 10 years, it would not be unreasonable for a customer to expect that everything should work correctly for at least the 10 years or even for as long as the life expecancy of the cables or accessories.
As a customer, I would not expect to have to purchase a warrenty to cover what should be provided as standard.