This may be of interest to anyone with tatty or out of date maps that should have been chucked out (most of us I think). OS are giving vouchers in exchange for old maps. The offer last until the end of April. It is worth checking on-line prices as well; I am not sure how the vouchers compare with some of the discounts available.
For more information see: https://www.ordnancesurvey.co.uk/shop/map-trade-in.html
The site I use for discounted maps is https://dash4it.co.uk/