During January The Woodland Trust has an arrangement with Tesco and WH Smith for the collection of your old cards. These will be recycled into new products, and the landfill credits accrued in your local area for reducing the amount of dumped materials will be passed to The Woodland Trust to benefit their work. Look out for the recycling bins in major Tesco and WH Smith stores.
For more information see The Woodland Trust website.
Please note that though printers do their best when sourcing from sustainable or recycled materials, proving the origin of board fibre takes a forensic laboratory and a lot of capital outlay and is not routinely undertaken!