Thanks for the reply. I am slightly confused as I attempted a dummy booking with the relevant avios and managed to get all the way to the payment page.

Can anyone else confirm this is true as my voucher expires on October - dummy booking was for flying late Nov returning Dec ?

I can only see this:

The upgrade voucher will be valid for 12 months from the date of issue. Your booking must be made within the 12 month period, after which time the voucher will expire and will not be replaced or extended.

Doesn't specify about traveling dates

Update: OK I just phoned them up and the lady confirmed that the booking needs to be done before the expiry date. Can travel after expiry date - not a problem