They're not, it's totally illegal, under EU Competition Law.
A cartel is a group of similar, independent companies which join together to fix prices, to limit production or to share markets or customers between them.
You need to file a complaint with the EU Competition Commission if you think the banks are stopping you from creating a Bitcoin business in the UK.
http://ec.europa.eu/competition/index_en.htmlCoinfloor was to be our best hope of a UK exchange, not sure what the hold up is, last I heard it was trying to sort something out through a Polish bank!
https://coinfloor.co.uk/God only knows when we'll ever be able to exchange £ directly for BTC!
For now all we can do is convert them into goods and services
www.takeaway.com Yum!

or use
www.localbitcoins.com