As I joined the 350 or so guests arriving at the Lord Mayor of London’s residence, at the Mansion House last night, there was little inkling of the disruption that was to come.
The City grandees, attired in black tie garb or elegant evening dresses, queued and chatted good-naturedly as they went through the Mansion House’s airport-style security before handing their coats and bags in at the cloakroom which stands immediately in front of the scanner.
Soon after the warm welcome for Chancellor Philip Hammond, events took a strange turn.
Barely two minutes into his speech, it became clear that a number of people had entered the room from the main doorway – perhaps 10, certainly no more than a dozen.
Most were women, all clad in red full-length dresses, not dissimilar to the ones being worn by the hostesses in the hall, the only difference being that they were clad with suffragette-style sashes, that read “Climate Emergency”.
There were only a couple of men and they were dressed in black tie and dinner jackets like all the other men.
An air raid-style siren was being played from a speaker mounted on the back of one of the men with a voice-over that said: “This is a climate emergency.”
One of the women moved down the aisle and began reading a prepared speech that was aimed at Mr Hammond.
A City of London Corporation employee blocked her from getting any closer to the top table while other officials sought to usher the protesters from the hall.
Another woman began reading a similar speech.
Others, as they were being escorted from the hall, threw rape alarms at the guests.
One landed below my chair.
They also distributed leaflets headed: “The speech we need in a climate emergency.”
The interruption was moderately unsettling but it quickly became clear, mercifully, that this was not a violent protest.
The treatment of the protesters that I witnessed was pretty gentle, to say the least, with most of the women being escorted from the room being taken out by other women.
I did not see the incident involving the MP, Mark Field, who was at the opposite end of the hall.
But I saw very little evidence of heavy-handedness.
The guests remained remarkably calm.
Most were bemused by the demonstration.
Contrary to what some people might think, most City folk are pretty liberal types.
Most of the guests who will have been in attendance are senior people in their jobs, by and large middle-aged men and women, who will no doubt in many cases, as they watched the protesters, have thought back fondly to the days when they too might have been protesters or student agitators.
Many will have sons or daughters at college and who come home at weekends and habitually lecture them on climate change.
They are aware of the climate change issue and will, in many cases, be engaged with tackling it as part of their jobs.
Accordingly, they were quite happy for the protesters to say their piece, provided they didn’t ramble on.
It was only when the protest looked like going on for more than a few minutes that a few guests started to lose patience with them and began to heckle.
Yet the whole affair seemed rather good-natured and typically English.
The City or London Corporation’s security guards were considerably more genteel than the bouncers one sees in a nightclub when trouble kicks off or at a boisterous pub at chucking-out time on a Saturday night.
As the last of the protesters left the room, Mr Hammond resumed his speech, noting: “The irony, of course, is that this is the government that has just led the world by committing to a zero carbon economy by 2050.”
His sally was greeted with a roar of approval.
It was ironic, too, that Mark Carney’s speech also unveiled a new initiative under which the Bank will, from 2021, begin stress-testing the resilience of the UK’s financial sector to climate change. It is a subject the governor clearly cares about deeply.
Outside, the corporation’s officials were trying to make sense of how the protesters got in.
The consensus was that an insider had opened a side door to the protesters.
The fact that the protesters had apparently even known what the hostesses at the dinner were wearing, so as to blend in, points to a degree of planning and inside knowledge.
This is a cause for concern.
The security at Mansion House was clearly overwhelmed by the Greenpeace protesters and, had the infiltrators instead been terrorists armed with knives or guns, there could have been severe bloodshed.
To that end, Greenpeace has probably done the City of London Corporation a favour, although guests at next year’s Mansion House dinner will have to remind themselves of that as they endure what will doubtless be a far more stringent security process.