Just had a long enjoyable weekend in Guernsey.
I didn't realise how near it is. As the crow flies it is a similar distance to London and flying in a plane means the journey is pretty damn quick.
The duty free, yes, no duty, is cheaper on the plane than at Southampton Airport. We could have got two litre bottles of Gordon's Gin or Russian Standard Vodka for £10 each. Instead, on the way back I got a litre bottle of Hennessey XO for £95, where a 70cl bottle in the supermarkets here is £135. I've never bought anything so expensive, or an XO before so I will savour it when I finally get round to opening it. We also got two bottles of Mumm champagne for £16 each. Cannot complain, so you must remember to not buy anything at Soton airport.