Now that sounds good, Jonzjob
This house had PVC windows put in by the previous owners. For the mot part, they work well. But there is a small casement window halfway up the stairs to one of the attics and I noticed a whistling draught coming from it during some high winds a week or so ago. On close inspection, it seems the window frame has not been put in very well - there is no draught sealing around it. Then the casement itself also doesn't seem to be a brilliant fit. The window doesn't have an air vent which in this particular case isn't necessary - the house is old and far from airtight !
My temporary solution was to fill the small recess with bits of foam, having stuffed newspaper around the worst bits of the window frame. It's certainly solved the problem for the moment - the main landing was always cold and now it's nice and warm !
The pipe insulation sounds a rather better way of dealing with the problem so we'll have a look at it when it's warm enough to remove my temporary barricade !