It it building work you need or just kitchen fitting and bathroom fitting? I can recommend fitters for both, who I used and were great. Wayne at SE1 Plumbing (07883 343408) has done plenty of plumbing & bathroom building for me, and Julian Gant at gants-service.co.uk did a great job fitting a kitchen in super quick time.
I just had a similar job done with my (nearly 20yr old) bathroom over a two week period in Jan 2017.
Yilmaz (07876 494 411) was the builder and you will find a number of positive recommendations for him on this site. Just a few things to add from my recent experience.
Planning phase - Yilmaz was very visit in the planning phase before we confirmed the job. I think he made three visits. The first one to discuss requirements and provide a quote, the second after I had put together an basic plan (with a list of things to be purchased) and a third one when the plan was finalised. His professional advice during the second visit made a huge difference to the way the final lay out. Yilmaz sticks to professional advice and doesn't really try and influence any design ideas. But he is good at pointing out when a design might not work (e.g. my initial choice of floor and wall tiles would have been incompatible where they meet near the floor). He also opened a couple of trade accounts so we can order things with a trade discount.
Timing - I gave Yilmaz a fixed two week window to complete the work and he managed to finish it within that period.
General discretion - the job was being done when I was away and I had no day-to-day control. But Yilmaz took all the deliveries, kept me updated throughout and also dealt promptly with a couple of unanticipated issues (the sink delivered by Ikea was broken which he exchanged and the flooring under the bath was rotting).
Pricing - I thought it was a perfectly reasonable quote and he stuck to it. Not a penny more.
Follow-ups - Yilmaz has made three follow-up visits. All of which he did at my convenience and without complaining. The follow-ups were to put some fixtures in and in one instance undo some damage that I had done to the wall!
He is also generally quite a likable and polite person. Feel free to PM me if you want to see photos of the job.