A fellow protester, wearing a blonde Boris Johnson wig, was handing out £350 million notes from the “Bank of Brexit Lies” to the crowd. One of the banners read “Who needs Airbus when you have Spitfires?”, but perhaps the most damning slogan was “If I’m here, things must be bad”.

A week is a long time in politics, as the saying goes. The prime minister has produced a plan, which unfortunately seems to have no parliamentary support whatsoever.

Brexiteers and remainers are united in their opposition to May’s proposal. It was refreshing to hear the former minister of state for transport, Jo Johnson – brother of Boris – admitting in his resignation speech that we’d all be better off staying in the EU than accepting the PM’s deal.

The choice, if the deal is rejected, is likely to come down to a no-deal Brexit or a second referendum, despite the fact Jeremy Corbyn seems desperate to avoid endorsing another referendum.

Brexiteers secretly hope we will simply leave on March 29 and trade under World Trade Organization (WTO) rules, but a no-deal Brexit would still have to be approved by parliament.

There are no WTO rules for travel and aviation.

Airlines would lose the automatic right to operate flights between the UK and the EU and the UK would not be under the jurisdiction of the European Aviation Safety Agency (Easa), which supervises standards and maintenance.

This could mean aircraft made in the UK would not have a legal basis to fly into international airspace. Incredibly, there is actually a government plan under which airlines would cancel flights two weeks before Brexit if there was no authorisation for them to fly. Passengers would get refunds, but not associated costs.

Ultimately, the pound is the best guide to the impact of Brexit. David Lamb, head of dealing at Fexco, a foreign currency business, said recently that “traders who typically spend their days poring over economic data have morphed into political pundits”.

If the politics of Westminster are just too difficult to read, it seems to me that the level of the pound in the weeks to come will give us the truest measure of how the markets and indeed the world at large is viewing this self-inflicted Brexit chaos.