I paid �3.5k a few years ago to get a small bathroom done. They used an independent contractor who did all the installation/plumbing/tiling himself. There was also an independent electrician.
It turned out that the contractor (inc. electrician) got paid �1000. The "parts" were �1500 which meant that Dolphin pocketed �1000 for sending round a "designer".
Moral of the story - ask people you know for a good plumber (they do exist) and/or builder.
I wouldn't use any firm who refused to deal with single women or any women whose husband is not present at the first meeting. I agree with the previous answer, get to know local trademen. I have just had a new bathroom installed and the local supplier gave me a list of names for plumbers.
I did a google search and found horror stories about Dolphin. So I used a local firm instead. In Wales, on a consumer TV prog, they highlighted caes of flooded homes, cracked tiles, badly fitted pie work etc, etc. It went on and on about their shoddy work.
I've just had my bathroom done by dolphin and I wouldn't recommend them to my worst enemy. There is nothing special about the materials they use or the way its installed either. For the amount of money you will be charged for the whole process, you would be better off asking around for a qualified plumber or builder and you'll get value for money and better workmanship.