Syria response is a challenge and test for Theresa May

Theresa May's flying Scandinavian tour - Denmark and Sweden in less than 24 hours - was supposed to be routine. As if...!

The prime minister's meetings with her counterparts in Copenhagen and Stockholm were wholly overshadowed by the alleged chemical attack in Syria: a challenge and a test not only for the Western powers and their allies, but for British global influence and for Mrs May herself.

As she met the Danish leader, Lars Rasmussen, in Copenhagen, it was clear she was keen to keep in step with key allies like America.

What was less clear was the likely form of any eventual British backing.

Logistical support - targeting or refuelling of attack aircraft - is an obvious possibility.

But a direct British attack would surely call for Parliamentary consent - and Labour leader Jeremy Corbyn surprised no-one on Monday when he called for a political and not a military solution.

In the event of such a showdown at Westminster, splits could emerge among MPs in both major parties.

Mrs May might well come out on top and receive the kind of endorsement denied to her predecessor David Cameron in 2013, when Labour sided strongly against British action in Syria.

But the prime minister has delicate judgements to make and this is yet more evidence that defining tests tend to be set not by politicians but by wholly unexpected events.