You would trade them for gbp/usd on one of the exchanges. Mtgox.com is by far the biggest. As for tax, this is probably taxed as any other profit you make on b

You would trade them for gbp/usd on one of the exchanges. Mtgox.com is by far the biggest. As for tax, this is probably taxed as any other profit you make on buying and selling stuff, at least in my country (Norway). If I buy an art painting and sell it with a profit, I am obliged to inform on this on my tax sheet. And the same goes for bying/selling other currencies as well, but bitcoins are harder to track for the government (but not impossible).