Trail-rat. They may not hold a retention but it depends on how much work needs doing.
f the proeprty is not habitable then it is likely in my experence that they will hold a full retention till the work is done. It may be possible to get access to the property to do the work between exchange & completion but this has its own drawbacks (vendor pulling out which hardly ever happens but no gurantees etc).
The valuer will normally ask to see specalist reports if its got damp etc and these will detail the cost of doing the work & the lender is very much guided by the surveyor & what they feel is suitable to hold back
If its not got heating but has hot & cold running water & an old wiring system then its unlikely they will hold a full retention & could just be the cost of getting the wrok done.
The trouble is that the higher the loan to value you need to borrow then the less margin the lender has if they need to repo the proeprty before the work is done so the more likely a retention is.
If its just general cosmetics then its unlikely they will hold a retention.
some lenders offer specific light refurb schemes so it might be worth seeing if you fit their criteria although IIRC the minimum deposit of these schemes is 15% - 25%.
Good luck