"There may be some mileage in challenging the legality of the agreement though"
trust me a firm of our size would not have allowed the BBC to film us if our contract was not legal!
There is a lot of false information flying around that what we do is in some way wrong and out contracts are not legal, if that was the case do you not think that we would have made them legal by now, we have only been doing this since 1923. Please don't believe all you read in the paper or on line as true. There is one firm that has been trying to control the market who only charge by the hour they have done a big campaign to say that the industry needs regulation, I agree it should be regulated. However in a lot of areas it is already regulated, F&F is regulated by ISO 9001 , ISO 27001, Data Protection ICO, AGRA, APG, Lexcel, FSO, and I am sure several others; our contracts are also regulated by the Trade Descriptions act, Consumer Protection (Distance Selling) Regulations and Cancellation of Contracts Made in a Consumer's Home or Place of Work etc Regulations.
F&F have been open regulation. I think there is a bigger issue to a firm that is not open to where research is conducted and how it is charged for than there is ever about agreements being legal.
I firmly believe that a % agreement is the fairest way to charge rather than an unregulated hourly charge when work is done on the cheap in India and charged as if it is done in the UK.