Are you building on at all? And will you be knocking through / needing steels??
We've just got costs back. We're in an expensive part of UK but not SE/London.
For something similar size - a full reno It was around 250k with a 10k contingency.
However this is with two knock throughs (so two 3 steels - inc one for the big sliders out ot garden. New windows to the front upstairs and down and side, new external doors to front and two sets of sliders at the back. New boiler and underfloor heating. Plus garage conversion
We didn't need rewiring but you well might. Rewire you're probably safe with thinking 15k
None of our walls outside of the rooms being knocked through (those ones will) needed replastering so that is a saving. We're just having them all skimmed. But again you may need a full replaster depending on age and quality of what is there.
This includes 2 bathrooms and a downstairs shower and a high'ish spec kitchen. Your pics are not medium spec kitchen. Neptune look is at the spendier end unforts. 50-70k is right depending on no of units. That would be appliances too tho.
We're also replacing all internal doors and skirtings as well as doing a full redecoration and reflooring throughout - wood downstairs and mid range carpet upstairs.
Landscaping was another 40k for what we wanted - got them to quote for that separately.
Also in that 240 is a full re-render and paint of the outside and new gutters - again you might not need that but there may be remedial external issues relating to brick work and damp which builders will probably want you to sort before you start with the inside.
I can send you a screenshot of the breakdown if you like?