Possible to fit double glazed units to single glazed UPVC?

[mikeelam]

We've got some double glazed UPVC windows and some single glazed UPVC windows of the same system in our house. But I don't know who made the windows or how long ago they were fitted.
Is it possible to get the single glazed units replaced with double? It would mean having the right, narrower, retaining extrusion to suit The new dg units.
Am in South London. Any help appreciated.
Thanks.

[stoneyboy]

mikeelam,
You've answered your own question - you will need to source narrower glazing beads. If the windows are more than a few years old you won't have a chance even if you could determine the manufacturer.
end