You might try
Newark. I don't know if they ship to the UK, but they do have several international sites. My local shop orders stuff from them, and it's where my Analog Devices chip was sourced (though I did not order directly).
Another useful site is
FindChips. It's a search engine that searches several suppliers' websites for parts. I believe most of the suppliers are in the US, but it's worth checking to get an idea of what a part should cost.