It's actually 2 things- the first one was a batch of old zips (priced in shillings and old pence) which were 3-for-10p. Total bargain.
The second is probably just as great a bargain- a Liberty pansy printed cotton skirt- which was only £3.49 from the local Bernardo's. It was elasticated at the waist, and a little long for me, so with a bit of sewing-maching magic, I took it up a few inches at the hem and added a proper waist-band and the zip at the back...et voila!
For lots of other excellent thrifted outfits, check out the Charity Shop Challenge Flickr group, and be sure to tweet your additions with the hashtag, #charityshopchallenge!