I came across this purely by chance when my wife Karen told me we had a few Tesco clubcard vouchers (I know, I know, I'm almost too embarrassed
to post this but it really is good!) Rather than just leave them I thought I would just use them on anything useful, anyway, while browsing the website I noticed a "Clubcard boost" offer from Evans Cycles, which doubles the value of your clubcard vouchers if you spend them at Evans. So I exchanged £7.50 worth of vouchers and got an e-voucher from Evans for £15! It is valid until 2016, so you can build these up as long as this offer is open. I have now done this twice and they are easy to use, they can be used as full or part payment, online or in store and there is no catch! Probably lost all my street credibility by posting this but who cares!