Hi, I just had a team of builders do my total loft renovation (it was about the same as loft conversion as we redid the roof, put in new steel beams, took out 2 internal walls, gutted out everything and put in everything new including a bathroom). I would highly recommend the guys who did the job:
Sergy +44 7960 187935
Ernest +44 7876 566763
For architect, we used Joe who was brilliant at advising what is possible and getting us planning permission. I can share his details. I can also share a brilliant structural engineer recommendation.
However, between these guys you need someone who will design the layout of your rooms, lights, bathrooms, switches, choose what floor you want, order the bathroom suite etc. Ernest and Sergy are brilliant builders but not designers. I did it all myself but it’s a lot of work (and I knew exactly what I wanted). It is cheapest that way, but if you are not experienced I would recommend someone who can do it for you (can be an architect or an interior designer).
You might also have party wall implications - if you were putting steel beams on the party wall. Structural engineer would advise on that. Again, I can recommend a reasonably priced and very good party wall surveyor.
If you decide to go down the “divide and conquer” route, let me know and I can send you more info. There is little point in engaging the builders until you have the plans / a good idea of what you want as otherwise they can’t price it.
All the best,