PERHAPS the most unbelievable aspect of a week which became more surreal by the day was the woeful performance of the official opposition party at Westminster.

Whether it was Jeremy Corbyn missing an open goal at Prime Minister’s Questions or John McDonnell’s inability to argue a coherent line on the question of Scottish independence, Labour’s performance at a crucial time in our history has been breathtakingly bad.

READ MORE: SNP join forces with other parties urging Corbyn's Labour to act

It has been the SNP who have put forward the most convincing arguments against the Brexit mess as it unravelled before our eyes.

As Labour floundered SNP politicians articulated the case against Theresa May’s cobbled-together deal and against the nightmare scenario of crashing out of Europe with no deal.

Despite the fact that Scotland voted with a healthy majority against leaving Europe, it has been the SNP who have pointed the way to the least bad Brexit ... one in which we retain membership of both the single market and the customs union.

That argument has been consistently ignored by Conservative politicians more interested in the internal divisions within their party rather than the best interests of the country.

And so it is we have a Prime Minister who is manifestly unable to find a way out of the mess her party has plunged us into.

No one seriously expects her to come up with an argument which convinces MPs that the deal she has negotiated is worth backing.

Yet Labour has shown no leadership, being unable to land a serious blow on a wounded Prime Minister, nor to stick to a convincing alternative to May’s terrible deal.

Corbyn should tomorrow listen to the suggestion put forward by the SNP and the other opposition parties at Westminster and act with them to scupper May’s deal and the prospect of a no-deal Brexit.

If he refuses and does not table a motion of no confidence in May’s government the SNP must do so.