Some types of benefit are not means tested, so they would still be available.
Means tested benefits would only be unaffected, however, if the 'improvements' were regarded as 'essential' to maintain the home 'fit for habitation'.
There's an excellent document - intended for the use of financial advisers - here:
http://www.cml.org.uk/servlet/dycon/zt-cml/cml/live/en/c ml/pdf_pub_misc_Equity-benefits-guide.pdf
(It's quite lengthy but it distinguishes clearly between means-tested and non-means-tested benefits. The most relevant part is about two thirds of the way down, under 'Repairs & Improvements')
Hoping this helps,
Chris