Hungary's Viktor Orban: Is one man blackmailing the EU?

The political rollercoaster that unfolded in Brussels this week was astonishing even for the most veteran watchers of European summits.

As EU leaders met for the last time before the Christmas holidays, all eyes were on one man: Hungarian Prime Minister Viktor Orban.

He is perceived as the Kremlin's closest ally in Europe, and is the only EU leader who met face-to-face with Vladimir Putin this year.

As his voice grew louder with threats that he would block two crucial decisions on Ukraine, speculation in Brussels was rife about how...