Timothy Murphy wrote:

We had all our large sash windows (16) restored
by The Original Box Sash Window Co (a UK company, I think)
about 5 years ago.

That is the job that I have to undertake.

They did a beautiful job, but it was incredibly expensive.
Fortunately the local council paid half (it is a listed building).

The local authority here won't contribute to listed building
rennovations - they just lay down the law about how the work is to be
done. Although TBH they know less about it than I do. I've removated
many sash windows in the past, but time is against me this time around
and I need to get the work done relatively quickly.

The company used the old glass in most cases, but made new frames.

We had some of the earlier windows in the house - some of them were
reclaimed 17thC windows re-used in an 18thC house - replaced a few years
ago. These were leaded lights. I got a local chap to remake the windows
using the old glass and he did a first class job. I had to fight the LBO
kicking and screaming all the way, she wanted us to use a particular
company who would ahve charged 4x as much for the work. I supected and
still suspect kick-back as the motivation for her preference.