At one end of Whitehall, the Government was solemnly announcing plans to add the direct action group Palestine Action to the UK's current list of 81 proscribed (banned) terrorist organisations. At the other end, its supporters were doing their best to muster a show of strength –while they still can. For once they are added to the list, alongside certified enemies of Western civilisation such as Boko Haram, Al Qaeda and Harakat al-Muqawamah al-Islamiyyah (that's Hamas to you and me), then this lot will qualify for mass arrests if they try a repeat of Monday's protest. For you don't have to be an operative or even a card-carrying member of one of these banned groups to be arrested. As it is, they tend not to be quite as hot on cards and membership subs as your average golf club. Merely being heard to 'express an opinion or belief that is supportive of a proscribed organisation' constitutes a criminal offence under the Terrorism Act 2000, a product of the early Blair years. I am not a lawyer but can confidently predict that Monday's principal chant – 'We are Palestine Action' – would fall foul of the law once that organisation joins the club. The Palestine Action leadership had originally planned a demonstration outside Parliament by way of reaction to the Home Secretary's response to last week's assault on Royal Air Force aircraft. Having broken into RAF Brize Norton, having made a mockery of the Ministry of Defence's pathetic security provision and having caused damage estimated in the tens of millions, this mob are now deemed to have crossed the line between direct action and sabotage. Had they tried this sort of wanton vandalism back in the days when the RAF Regiment patrolled air bases with live ammunition, we might have been covering a funeral on Monday. As it was, it seemed inconceivable they would be allowed within shouting distance of Parliament. Sure enough, the police had restricted Palestine Action to Trafalgar Square. There were at least 500 of them, and they managed to bring much of central London to a halt by blocking all southbound traffic. A little after midday, I saw a No 29 bus stuck next to the church of St Martin-in-the-Fields. The driver was still there nearly three hours later. At one point the bus became a refuge for a brave counter-demonstrator who arrived with an Israeli flag. The police were being called every name under the sun but remained calm and in regular 'soft' uniforms and hi-vis bibs. Periodically, a snatch squad would wade in and haul out a protester amid much synthetic outrage from the rest. 'Let him go!' chanted the herd, while a little flock of self-appointed busybodies in 'Legal Observer' tabards fussed around, desperate to record evidence of police heavy-handedness (I saw none). Those stuck in the traffic for several hours on another sunny day will have thought: 'If only.' If the police were at fault Monday, it was in letting the capital remain gummed up for hours. I have to say that I did not feel I was in the midst of terrorists. Deluded, obsessive, ranty, repetitive conspiracy theorists united in a pathological loathing of Israel, Donald Trump and British foreign policy, perhaps. But the prevailing vibe was more Lib Dem conference than jihadi. We had plenty of students, of course, but if one demographic could have been said to predominate, it was the recently retired white middle class. For every protester in a hijab, I could count three grey-haired (or bald) baby-boomers dressed for rambling, save for the Palestinian keffiyeh over the shoulders. Perhaps I am guilty of crude generalisation but then I can only say the feeling was entirely mutual after I was twice accused of 'supporting genocide' on the grounds that I was wearing a linen jacket. I met an articulate retired scientist who said he could see nothing wrong in crippling RAF aircraft which, thus, can no longer defend the realm. 'They have been complicit in war crimes,' he told me matter-of-factly. At the start of the demo, a group of young mothers laid a rainbow-coloured blanket on the road and encouraged their children to do some drawing. Drums and megaphones kept up a modest din but we had no stage and no 'keynote speakers'. There was also a notable Irish flavour to it all – plenty of Irish tricolours and slogans plus a sound system pumping out rebel songs like Come Out Ye Black And Tans. After two and a half hours, several vanloads of rather different police eventually turned up with helmets and body armour and methodically cleared the road, scooping up a few more road-blockers for arrest. After a few squawks of 'fascist!', the crowd started melting away. There in the mix, I spotted Piers Corbyn, swivel-eyed bonkers elder brother of Jeremy. No lost cause is truly lost until Corbyn Senior is on board. He was wearing a 'Resist! Defy! Do Not Comply!' T-shirt on Monday. By teatime, compliance was complete.