It the most significant move on Brexit in politics since Theresa May appointed the Three Musketeers of Brexit – Boris Johnson, Liam Fox and David Davis – to top cabinet positions.
Chuka Umunna has now pinned his theses to the front door of the Labour’s HQ by announcing that Britain and especially London must stay in the single market and customs union in order to preserve foreign investment and economic activity.
And Umunna has shown real leadership in making clear – politely, in his non-abrasive and inclusive manner – that the endorsement of the Tory-Ukip line that Brexit means leaving the single market and the customs union cannot and should not be sustained as Labour policy once the election is over.
Jeremy Corbyn knows very little about the technical details of Europe. He has subcontracted European policy to lawyers who end up with the self-contradictory policy of wanting the benefits of the single market (they’re unsure on the customs union) while advocating putting up barriers to fellow European citizens living or working here.
Corbyn’s statement that free movement will  end and be replaced by “managed migration” is Labour’s version of Boris Johnson’s having your cake and eating it. This is what all Labour’s sister parties in Europe have rejected – namely that the UK can cherry-pick the bits of Europe it wants but have an exception on other common rules and laws the EU27 agree to live by.
Now Umanna and other London Labour MPs have cut that Gordian knot by recalling Nye Bevan’s maxim that the “language of priorities is the religion of socialism.”
Umunna is prioritising jobs, investment, trade, and the economy over the obsession with immigration. Four per cent of Ireland’s population is Polish, a far higher share of the Irish population than the Poles in Britain. 1.2 million Romanians live and work in Spain, which has a population of 38 million. You can scour the Irish or Spanish press or read all the speeches of Irish and Spanish politicians and you will not find the kind of ranting hate against European citizens in our midst that has been the norm in England this century.
Enoch Powell elevated anti-immigrant populism to the top of the political agenda nearly five decades ago. It was stamped on hard by the political and media class but once the immigrants became white Catholic Europeans from the late nineties onwards it was possible to use all the Powellite tropes again – and every Conservative leader from William Hague onwards did so, with increasing support from the Europhobe press.
In short, the hate against immigrants that won the Brexit vote last June is a made-in-England political project that other countries with far more European immigrants have avoided.
Instead of falling into the Ukip-Tory trap of aping their demands for physical Cold War era controls on citizens of 27 EU member states like work and residence permits, seasonal or regional allocations or cruelly saying a worker cannot live with a spouse and children, Umunna is pointing out that there are many ways within single market rules to control immigration.
The best way is to promote jobs for British citizens. Freedom of movement does not apply to state employment. But Britain refuses to train enough doctors, nurses and other medical staff so 140,000 Europeans work in the NHS and care sectors looking after us.
Identity cards are the uncontroversial norm in all EU member states, some with much stronger libertarian traditions than we have, and their existence ensures an employer cannot hire someone without knowing who he she is. The EU directive on agency workers could be rigorously enforced to stop the mass hiring of Eastern European workers via gangmaster employment agencies.
It is perfectly permissible to limit access to benefits until such time as a newly arrived worker has made appropriate contributions and, as Chuka Umunna pointed out on the Today programme, it is legal under EU rules to deport someone who has not found work after three months.
If Nick Timothy gets his way and Theresa May adopts an Erdington vision of workplace relations after the election, he will know that trade unions in Birmingham’s metal-bashing industries played a key role in partnership with employers in hiring practices and sought to help local workers in their communities.
These internal controls on immigration can be put in place in full conformity with staying in the single market. Chuka Umunna has shown real intellectual and political leadership. He almost certainly speaks for many more Labour MPs than dare join him now, for all LibDem and SNP MPs and for more Tory MPs who also realise that leaving the Single Market and Customs Union is quite crazy but do not yet know how to say so in public.
Denis MacShane is the UK’s former Minister of Europe and a Senior Advisor at Avisa Partners.