If Britain can no longer be a member of the EU, it will benefit from being as close to Europe as possible

The ceremony in Rome to mark the 60th anniversary of the founding Treaty of the European Union is a sombre moment to reflect that the forces pulling the peoples of Europe together are stronger, in the long run, than those pulling us apart.

Sixty years ago, there were just six countries coming together. The UK, having made its lack of interest clear, was not invited. Today, 27 countries affirmed the unity of most of the continent and the UK was again unrepresented. For most of the intervening period, we were in, with varying degrees of commitment. Viewed in the long lens of history, who can doubt that Britain will be engaged in the decades to come, with varying degrees of commitment, with the European project?

Those passionate believers in the ideal of European unity who marched in London today should take heart from this longer view. The Independent sympathises with the view expressed by Tim Farron, Caroline Lucas, Tony Blair and Alastair Campbell that Britain’s departure from the EU can and should be stopped. However, that would require a sustained and significant shift in British public opinion in the next two years, which may be more likely than the Prime Minister thinks, but which is still not likely to happen.

While fighting to persuade people that Brexit is not in their interest, therefore, pro-Europeans should also prepare for the battles to come. Over the next two years, Theresa May will be negotiating the terms of our relationship with the EU, and The Independent will be making the case that it should be as close as possible.

In this venture, we have allies among the EU 27, and among their elected representatives. Guy Verhofstadt, the chief negotiator for the European Parliament, tells us today: “Both the UK and the EU stand to lose from this process, which is why we must work to mitigate the effects of the decision that has been taken.” This is a rather different tone from that adopted by Jean-Claude Juncker, the European Commission President, who this week said: “Britain's example will make everyone realise that it’s not worth leaving.”

Of course, we understand that our European partners cannot allow Britain to enjoy the benefits of EU membership without contributing to the common welfare, but Mr Juncker was unwise to use such language. Mr Verhofstadt is more in the spirit of European unity in emphasising the benefits to both sides of the closest possible relationship.

As Ms May prepares to sign and send the official letter of notification under Article 50 of the treaty that started off as the Treaty of Rome, that is the pressure that must be brought to bear on her – and on her opposite numbers. Mr Verhofstadt makes it plain that he sees a “reciprocal agreement to safeguard the rights of EU citizens in the UK and UK citizens in the EU” as the immediate priority of the negotiations. Again, this is different from other EU leaders who have suggested that Britain’s “exit fee” should be the first item on the agenda.

It will require heroic efforts to avoid the negotiations slipping into negativity and hostility, but there is goodwill (and a healthy dose of self-interest) on both sides and today’s marchers for European unity need to encourage both sides. At the minimum, we must try to avoid leaving the EU without agreement, but Ms May should be more ambitious than this: the closer our relationship with the EU the better.

Maybe in 2057 a British – or possibly English – prime minister will be invited to the centenary celebration in Rome.