Where to start?

[cnca00]

We have an old unheated conservatory on the back of our kitchen which is too hot in summer & too cold in winter. Kitchen is also old and needs replacing. We were thinking of removing the back wall and incorporating the conservatory into a new kitchen diner, either by putting on one of those 'warm' roofs or knocking the whole conservatory down and building a proper extension.

Trouble is I've no idea where to start! Who should I contact -

An architect / conservatory roof company / builder / structural engineer / council for planning permission?

An architect or planning consultant. If you're in London we used PlanHub and they were good. Either of these can help you understand what's possible. Once you are happy with the plans, the council will need to give you planning permission or approve your permitted development application (again, a planning consultant or architect can help you understand which you need). From there, you'll likely need a structural engineer.

I used a company called home tales for my ground floor extension and they have architect, planning and engineer in a design package. They were excellent and gave me loads of advice before I began which was super helpful! www.hometales.co.uk

Prices per sq metre vary across the UK, but ball park , you’re looking at £1500 to £2000.

We had a “technical drawer” come around to discuss extension at the back. He gave some great advice about issues we’d have with the garage roof line meeting the extension roof, costs involved to avoid that.

Do you have a vision of what you’d like it to be when finished, size wise I mean?

Your local council website will have advice on what is permitted without planning permission and what the costs and requirements are if you wish to proceed. They also detail planning applications and usually show plans if you want to get some ideas.

I can understand you eagerness, but take your time. The area (kitchen) is an important part of the property so go as big as you can both financially and physically. Get ideas from professionals / magazines / friends etc and mull them over. Don't commit to the first idea you arrive at.
Personally I would not try to integrate the existing conservatory into your plans. They are generally not fit for purpose as part of the main structure. Get an architect to create a plan and schedule for your final idea and then get 3 written quotes.