wrote:
I live an old house with sash windows. Is there a cheap and easy way
of stopping wind coming through the space where the top part slides
over the the bottom one?

This type of sash fastener, if properly positioned, should pull them
together.
http://www.diytools.co.uk/diy/Main/P...ProductID=6505

It would also help if the solution was such
that it stops the two parts banging into each other when it is windy
outside.

If you mean when they're open, a piece of folded cardboard. Very hi tech
I know, but the only thing that works


I was wondering whether insulating strips could be attached - but am
worried that they will be very difficult to fit and will stop the
windows sliding properly.


Tried all that. I wouldn't bother. Anything spongey will tear and
disintegrate. Anything springy, like the v shaped plastic will soon stop
springing. Brush strips work well but then you're into major renovation.
Setting the staff bead tight to the lower sash can stop a lot of draughts.