The "conflict" has been going on ever since the Berezovsky received asylum in the UK. He continues to fund activities against the Russian government, but the UK refuses to extradite him. The reason all the politicians in the UK freaked out over Litvinenko is that it puts London's reputation as the leading safe haven for defectors/dissidents/mafiosos and their money in doubt. A big reason that London is the world's financial capital is that it is also the world's money laundering capital.

Of course none of this applies to people like Assange because they don't have any money or come from countries the US doesn't like.