If you need list about buy bitcoin in UK, you can find it here : http://www.coindesk.com/information/buy-bitcoin-uk/
The ones that you might want are LocalBitcoin and Coinbase.
Thanks, but I'm not looking for any method to sell bitcoins, but for the cheapest and most convenient way to sell rather small amounts ( <£100) quick and hassle free, something that have all/most of the features listed in the first post.
Localbitcoins is not what I'm looking for, as it's too complex and time consuming for small value txs. Coinbase requires id verification and I'd have to convert EUR -> GBP every time, which generates extra cost afaik (their fees look reasonable though).