At my uni it would depend what type of postdoc you managed to get - an RA starts around £25K and an RO at c£29K up to £34K so it does vary. I think junior lecturers are on about £32K - either way its nice money. To put it into context in holiday between ending my BA and starting my MA I had a p/t job in a shop - I earn only £20 less now for a 5 hour day than I earnt in an 18 hour week a couple of years back!