Adding a new bathroom to flat--which type of builder to use?

Well Kay, if they turn up in wellies and waterproofs they might not be the right ones!..lol Joking aside, Like ourselves you want a builder/company that can provide past experience and references you actually can check out, do it there and then while they are with you, put them on the spot. Do a bit of research yourself, then ask questions see if they have the knowledge, like what size pipe do you need for the waste on your basin?..what IP rating does your extractor need to be? Most of the time you can tell be the person and their knowledge and all the above if they will be the right fit for your project, but do not be intimidated If you don't get the feeling then do not be afraid of saying thanks,but no thanks.

A general builder will be the best as they will have access to multiple qualified trades men required to do every aspect of the works

For a job like this you would need someone who has experience in many areas of the building trade. plumbing , plastering, tiling, first and second fix carpentry, somebody who takes pride in achieving exactly what the client wants. They need to be a true multi trader ,able to get the finish and wow factor that's expected from an experienced multi trade builder.

A good general builder as they normaly have the connections to get the job done from start to finish.

You would need to employ the services of a building company such as ours that carry out all works and can provide the relevant certificates upon completion such as gas/electrical certs.

To add new bathroom some times isnot as simple as it sounds . Its all depends on what's the clients budget is . Before go any further . How far your new. Bathroom from new one. How far the soil stack from proposed Bathroom . You need hot and cold supply , all electrical work . Window in proposed bathroom need to be altered. In some cases building control need to be informed .