Lots of good points made by others as to the practicalities and house-value of taking on a domestic basement project.

I would therefore add a professional point of view as a construction project solicitor. Please take early and specialist advice on the contract (long) before you sign it, to ensure that you know what is going to be paid, when, and how and why extras are added (or not), and valued. Whether you're spending what you are going to on a complicated project like a basement in a cramped residential area, there are significant liability issues at stake. Each has his/ her own expertise, make sure you've got yours on side acting (solely) for you. You also have duties to neighbours, including party wall and subsidence. Project and works insurances can be complex too. You also need to consider longer term liability (i.e. your legal position once your builder has left site), because issues can take time to settle and manifest themselves.

We can help to navigate through this minefield which all revolves around the contract, and we can support you at early stages (before it gets full-on) to tackle and assess these difficulties, and draft terms to protect you from challenging surprises - because there will be some. In 20+ years of specialist practice, I can hand on heart say that however well you're briefed by the builder and engineer, however much planning you your self do, the contract arrangement is not set up properly in the majority of cases, and there are always unexpected events, and so there are unbudgeted costs and frustrations for everyone.

Good luck, and please DM for specific advice.     

we're looking at extending the house at the moment and we're working with Harriott Eyles (google  them under Ha-Ey) they're an architecture + engineering practice that have loads of experience in basements in Fulham and Hampstead, that I know of. Might be worth contacting them? Best Wishes Jola 

so what do we think the cost of the square footage cost for half-footprint on a terraced house between the common please? we are also going through the exercise.
also we have been told that it's not possible anymore to have the front light well openup and it has to be glazed, is that correct ?
thank you

@BTC_Mum
When you say half footprint, what sort of square footage was that? I'm trying to work out what the rough costs for a basement are at the moment. Thank you

Sadly the days of a basement adding value to your property are long gone
The cost of the building is far greater than the value add.

We looked last year and the cost of the full footprint extension was around £600k, which would add just £400k to the value
A half footprint was around £350k and would add around £200k

So the main advantage of doing the half footprint is that you don’t lose as much money..!

It is also worth thinking about if or when you are likely to move. The feedback we got from estate agents is there is less buyer demand for very extended terraces
So a standard BTC house with a full basement is going to have an asking price of £2.2-2.5m, but there aren’t as many buyers for those houses as there are for under £2m, so it will take longer to sell when you come to putting the house on - months rather than weeks for a smaller house

Hi - if you are going to go to all the fuss and bother of, architects, engneers, building control and planning permission- to mention a few - you may as well go for a full basement- even if it means doing a mortgage to complete- the value appreciation to your property will be worth the effort - even if you just get all the planning approved - that in itself will add value to your property

Decided over the holidays that this is something we would like to start planning seriously for.

Wondering if those who have done either of these options would be happy to share if they are happy with what they chose. There is non surprisingly a big difference in price between doing a half and full footprint basement and wondering if we would regret stopping at the kitchen i.e. just going under the front half footprint. Any recommendations also much appreciated. Thanks so much!