As soon as we heard of plans for the Unite for Europe march back in January, we decided to be part of it. It wasn't that we thought it would change anything, just that sometimes it's important to stand up for your beliefs and to make common cause - or commiserate - with those who share them. Besides, we could make a weekend of it, perhaps see a play, enjoy a meal out.
Thousands of others clearly felt the same - perhaps about the theatre as well as the march. These were not seasoned protestors - no anarchists-for-Europe broke away to trash the Ritz as we paraded past. With the Brexit-supporting SWP out of the game, a single well-spoken Trot from Socialist Appeal had cornered the market on Park Lane.
This was a particularly British affair - not so much a march as an orderly queue, less a protest than a rather severe ticking off. Some of the more industrious must have been up all night designing their placards. Heaven knows what alternatives they rejected, but some of the slogans were argued in such detail that it took the length of Piccadilly to read them. The best - "I am quite cross" and "Tut" - summed up the mood rather more succinctly.
So there we were in the brilliant Spring sunshine, a sea of mostly white, middle class, middle-aged, middle-English liberals in polite pursuit of a lost cause.
That observation is intended neither to invalidate the purpose of the protest nor denigrate those who took part. Relative privilege is no bar to strong principle.
Nevertheless, the march perfectly illustrated how the referendum was lost last June and why little has changed since. Those who believe in the European ideal have failed to convince those who don't, many of them less economically secure, less well educated, less politically motivated. The placards and the speeches in Parliament Square reminded us that Brexit will rob the next generation of their inheritance. Yet, though there were young people in numbers among the marchers, there should have been many more.
And where were the political parties which, even if they failed to make the case for the EU before the referendum, should have been leading the campaign against a hard Brexit since? To their credit, the Liberal Democrats, under their placards and in their yellow favours, were out in such force as they can muster. But shamefully the Labour Party was all but invisible and pro-European Conservatives were nowhere to be seen. No member of the Shadow Cabinet - much less the Leader of the Opposition - stood on the platform, no leading Tory Europhile spoke.
Though speech after speech rehearsed the reasons why Brexit spells disaster, no-one really had a plan to stop it. But then we weren't really expecting one. Perhaps this was just a form of group therapy, a two mile stroll in the fresh air with sympathetic companions followed by some well-meaning but ultimately ineffectual counselling.
Lessons from the Beyond the Grave
Next day, we decided on a whim to visit Highgate cemetery and it was there that the point and proper purpose of the march dawned on me. There among the remembered dead were men and women of all nations and all convictions. Many had sought refuge in Britain and contributed to its economic, cultural and intellectual prosperity long before the EU had been conceived. Many had come since, exiled from eastern Europe, Iraq, Afghanistan, China; there were Jews, Muslims, Christians, atheists. The ashes of the social Darwinist Herbert Spencer are interred almost directly opposite the tomb of Karl Marx.
There is no reason why Brexit should mark the end of that tradition of openness, sanctuary and free thinking. If the march spelled out one clear message, it is that millions of Britons believe in something nobler than narrow nationalism and that for them being members of a compassionate, tolerant and democratic society defines who they are and want to continue to be. It may be harder now, but there is no reason why we cannot sustain and build on the UK's claim to be that kind of society. That ideal has not been defeated.
Had I addressed the crowds at Parliament Square, I would not have pretended that simply by being there, we could change the country's course. But I would have wanted to identify a challenge to which we could collectively rise. Now I know what I would have said.
Even if Brexit cannot be stopped, the greater cause is not lost. We do not cease to be citizens of Europe - or the world for that matter - by a stroke of Theresa May's pen. It is still within our power to determine what kind of country Britain will be, so long as we can persuade a majority of our fellow citizens that our values are also theirs. This we failed to do last June.
Now we know what must be done. The like-minded marched together in London on Saturday and no doubt felt better for the experience. But if we want to make a difference and uphold the values we fear might otherwise be lost, we have to reach out to those who were not there. If each of those who supported the demonstration makes it their business to persuade perhaps just one sceptic that peace, partnership and open-mindedness are prizes worth marching for, we might rescue something important from the wreckage that Brexit threatens.
At the base of Karl Marx's tomb is inscribed his precept that "the philosophers have only interpreted the world in various ways - the point however is to change it". Like the EU, he wasn't all right. But nor, like the EU, was he all wrong.