Corbyn's win has taken Britain a big step closer to an exit from the EU
The election of Jeremy Corbyn on Saturday as the new leader of Britain's Labour Party has just made the task of keeping the UK in Europe so much more difficult.
Corbyn's election has obviously delighted the British Left. His passion for renewal of Labour after the Blair/Brown years is not in question. He comes across as a very principled and honest man and has been around Westminster for a very long time.
But much of his rhetoric comes across as dated. At times, he seems unable to come to terms with the intense complexity of a modern and global system that is so interconnected.
The world today and the politics of modern government are not defined around polar opposites and simple choices from ideological textbooks.
The world has moved on from the 1960s. Governments, especially within the EU, operate and govern across member states and in a multilateral setting. The options they face are limited by economic activity that is itself global in nature.
Just look at the City of London and the financial market that is such a power house of activity for the UK. Whatever Jeremy Corbyn might want to do for Britain, much of it will depend on China or Asian financial markets. Britain is no longer the industrial and manufacturing capital of the world. It depends on the emerging service industry and finance, especially for much of its new wealth.
And that sense of unreality, which his election brings with it, has two really damaging consequences for Britain.
One, the Labour Party now looks pretty unelectable for the next general election. And two, the amazing enthusiasm of Corbyn's supporters will inevitably turn to disappointment as he simple cannot deliver.
Yes, people want something different and much clearer lines of differentiation in politics.
But Corbyn needs to remember that in a 40-year period (1980-2020) the British Labour Party has been in office for just 13 of those 40 years. It did not win from the Left in 1997.
And only when the party had Tony Blair as leader with a centrist policy platform did it win elections back to back. It was Tony Blair who won three Labour victories, not Tony Benn. This new leader looks more like Benn to me.
It is beyond doubt that the British Left has been empowered by Jeremy Corbyn's victory, but frankly you cannot win from the Left alone. Whether his victory will delight the British centre ground, the people who really decide elections and show an appetite to move from one party to another, is quite another discussion.
Jeremy Corbyn's election is also a huge fillip to Nigel Farage and the eurosceptic cause. The anti-European element in Britain has always believed that the only way it could win on the question of an in/out referendum was with a divided Labour Party.
It now has that.
Jeremy Corbyn is manna from heaven for Nigel Farage and other eurosceptics. His election opens up the prospect that none of the main parties in the UK, except the badly beaten Lib Dems, can describe themselves as totally in favour of Britain staying in the EU. It's a very dangerous state of affairs with the vote expected by April of next year.
The most fascinating question of all now, when the referendum comes, is what will the new Labour leader do? Without a united Labour Party arguing for Britain to remain in the EU, the referendum looks doomed just as the campaign is taking off.
David Cameron knows that the anti-EU element in his own party is a major threat to a successful referendum result.
I've written before that the British decision on Europe is the biggest foreign affairs challenge we in Ireland have faced since joining the union in the 1970s. It's in our strategic interest that the UK remains in the EU.
The implications of a British exit are enormous for Ireland.
Jeremy Corbyn's victory brings the day of British exit from the EU even closer. We are entering a very dangerous period in our relationships with the EU and Britain.
The need for that famous contingency-planning unit in Merrion Street, which has the task of working out the implications for Ireland were the British to leave, has suddenly moved up a gear or two. We had better prepare for the worst outcome because the omens certainly don't look good.