places like 7 day shop are cheaper but you will probably wait 7days for it to arrive.I live in the sticks so that's why I pay for prime. If you can get it through work all the better.
Try this next time, 16GB £13.99 delivered Friday, (tomorrow) https://www.amazon.co.uk/SanDisk-16Gb-SDHC-SecureDigital-Capacity/dp/B00422F8XQ/ref=sr_1_2?ie=UTF8&qid=1309432842&sr=8-2