On one level, the widening diplomatic spat between Britain and Russia is entirely predictable. It is a ritualised dance of mutual defiance that will reach a peak, and then subside. It was always thus in the days of the cold war.

On another, it is a nasty sign of the general deterioration in Russia's relations not just with Britain but with the European Union and the US, as President Vladimir Putin has reinstalled the dominance of the security services over both government and business.