thanks for the replies, i plan on resisting it for all the reasons you have mentioned above, apart from just security reasons its a very valid point that the contractor is hired by the insurance company to complete the work cheaply rather than to my satisfaction.
it just seems like bully tactics that if i cant get a builder to do the work for 6k they will get one that can.
Read your policy. This is the basis of the legally binding contract that exists between you and your insurance company. The policy will probably outline that insurers at their option can indemnify you by reinstatement. This means that they can if they so wish bring in a contractor to do the work to your home. If the policy doesnt outline this, then Insurers cant affect reinstatement. However, I am assuming that on the basis of what you said, the policy does have this wording.
You bought that policy. If that wording is in the policy document and if you had a problem with it, you shouldnt have bought it. If you plan to resist it, then you could find yourself in breach of the terms and conditions of your policy and in such cases, you may void the policy. Be careful how far you plan to resist it. You may feel that you are in a position of strength morally, but in accordance with your policy, you most likely do not have "a leg to stand on".
Insurers invoking the terms and conditions of the policy is not bully tactics, insurers are merely doing what they are entitled to do in accordance with the terms and conditions of the policy. The policy will indemnify you by reinstatement. This means that you are put back in the position following an event that you enjoyed immediately beforehand, but as new. Satisfaction is a subjective thing and as long as Insurers reinstate to the appropriate level, they are fulfilling their contractual obligations.
Contrary to what people think, Insurers panel contractors are fully vetted and checked by insurers before they are allowed to carry out work. They carry all the relevant insurances etc.
If you are in any way unhappy with the way you are being treated, there is a complaints procedure and indeed, you can ask that your complaint be referred to the Insurance Ombudsman, who will give a binding ruling, which if you dont agree with, can be subject to an appeal to the High Court.