I work in a Post Office and we offer a banking service to most banks customers, NatWest, RBS, Barclays, Lloyds TSB, Halifax, to name a few, the only major bank we don't deal with is HSBC. If your bank is one of those we do deal with you can withdraw cash free of charge (some shops will charge 50p or £1 to get cashback) and you can withdraw any amount from 1p up to whatever your cash card limit is (usually £250 or £300 a day). So if you want to withdraw £2.21 you can do.