WWW.londonsashworks.com. Steve does an excellent job, competitively priced.

London sash window repairs. (https://londonsashwindows.com/)

we recently used them to replace all our sash windows, which also includes draught proofing. They finished to a very high level, were tidy and competitively priced. 

Hi all

Can anyone recommend a local draught proofing service for sash windows - there's a couple of threads on here but fairly old now.

Thanks!