Re: "between 2007 and December 2014"
I'd never be stupid enough to sign a contract like that.
Fixed payment for an entire project is a mugs game. Can only be time and materials, otherwise the risk of being paid 1 year of time for 5 years of work is way too high.
Only organisations like Capita can afford the army of lawyers needed to enforce payment-by-change-request, a lone contractor can't.
Yes, PAYE contracts could be used, but many clients refuse to do that because they would also have to provide the benefits of being an employee. IR35 is great, because the client can make you an employee for tax purposes and a contractor for rights purposes. Everyone loses! Yay!