Last year when I claimed for a flight delay against Thomson I finished up with CEDR and had excellent service. It will be interesting to see what the process of claiming is.
In my case I had to first submit a claim to Thomson which I did using Resolver which is FREE. At the end of the process I was referred to CEDR - having used Resolver the documentation was easy. You can also ring CEDR if you have any difficulty when submitting your claim and they will assist.