Side return extension - builder recommendations?

[Martinva]

I am looking to extend out the back and side return on my Victorian terraced 1 bed, ground floor flat.
I have read several horrifying threads on local mum's hubs about a couple of building companies I WAS considering (and thank you to those thoughtful people have taken the time to share their ordeals)
But wondering if anybody has been through it and had a positive experience? if so, please could you share?
I am after a building planner or architect initially, but would value any feedback on building and construction companies too.
Thank you in advance!

To be clear, I work for a construction company (I'm not promoting it on here) in London - your area may be different but here's what I'd suggest. Meet as many companies as you can and rely on your gut instinct. I sometimes feel contractors forget you've handed over your most valuable asset to them. Also, you're going to be dealing with them for months so you must get on and feel comfortable. Even the slightest 'off' feeling and move on. Get personal recommendations but do bear in mind that there might be one rogue job that doesn't reflect the builder if all other recommendations are good.

Questions to ask:
Do they sub-contract out their jobs? You may just meet a 'sales' guy who then farms the work out - this is OK provided you get on with the subbies.

Who does the plumbing/electrical work? In-house guys or subs? Will they issue electrical and gas safe Certificates?
Will they deal with Building Control and who do they recommend for this (I'm always suspicious if a firm really pushes you to go private or with their building control company - council is fine and they're protecting your interests too).
What's the payment schedule and retention for snagging?
Will they provide a works schedule?
Will the team change? Who will be your primary point of contact? How often will site meetings be?
Guarantees?
Can you meet previous clients and see their work? This shows they have good relationships with their clients.
Get a detailed quote and drill down on what the spec is for any goods supplied such as radiators, light fittings etc. For instance, we charge per standard radiator inc valves and fit. What you don't want to see is a line for 'central heating' and it's unclear what this includes or what type of radiator. Also check on insulation and acoustic plasterboard given you're a terrace. Actually, talking of which you'll need a party wall surveyor, too. Finally, a good builder should know enough for you to only need a technician for drawings. PM if you want to ask anything in terms of process prior to build. Good luck!

Where are you based?