Passengers packed onto an EMR train from London to Leeds on Saturday afternoon following the announcement that London was about to be placed in Tier 4 restrictions - a new, tougher level of Covid measures - from midnight.
But many passengers were shocked to discover, once they boarded the service, that too many tickets had been sold to allow social distancing to be observed safely onboard.
An announcement on board the train from London to Leeds told customers that social distancing was not possible onboard 'due to overcrowding', and instead asked people to wear a face covering.
One customer who boarded the train in London explained how the confusion arose, leading to packed out trains leaving the station.
They said: "When I bought my ticket, I assumed there would be very limited numbers and everyone would have a seat allocation.
"It wasn't until I got there and we started boarding the train that it was clear there was too many people and I can't get my head around how that could happen.
"You'd think no tickets would be left after a certain point, because at the queue for the gates, while there was a lot of people, there were two trains going very close together so it wasn't clear how many people would be on each train."
EMR suspended reservations in March and allows people to buy walk-up tickets. That is in contrast to LNER, which only permits people to book reservations and refuses any further passengers when the reserved tickets are sold. EMR is not currently running a reservations-only system.
EMR said it could not switch off its walk-up tickets sales at short notice. Now, the company has promised a review following the incident.
EMR spokesman Andrew Commons told the Yorkshire Post: "What happened last night was a complete one-off. We run one train a day London to Leeds and we always have. That's because it's a team that stays overnight in Neville Hill in Leeds.
"It was a direct knock-on effect of that Tier 4 announcement. We do continue to sell walk up fares, but last night was the first time this has happened since March 23.
"We had no more notice than the public and we can't turn off sales in two hours. You can buy them at the station, you can buy them online, at the machines... there is no way for turning off sales that quickly.
"That created a one-off that people piled onto that particular train after the announcement.
"LNER are reservations-only so they weren't accepting anyone else on their train.
"Last night we rain 11 or 12 trains out of London and two of them were full.
"That one train to Leeds was an issue because of the announcement. Everyone got three hours notice, there were similar issues at Paddington and Euston and everyone was in the same boat.
"It was just a vagary of our times, we run one train all day from London to Leeds and everyone wanted to get on it."
Mr Commons added that the reason the train was swapped at Derby was not to create more social distancing damage by swapping people, but to allow for customers to board a bigger train.
He added: "We will definitely have a review of it tomorrow. We have a situation where some trains are reservation-only and some aren't."
He also said that trains had only been running at 8 per cent capacity through the year until this 'one-off' service.
An East Midlands Railway spokesperson, said: "We appreciate some of our services out of London on Saturday evening were much busier than normal and we are sorry for any inconvenience and discomfort caused to passengers.
"We want to reassure everyone we are already running our full, pre-Covid, Intercity timetable with as many trains and carriages in service as possible and we are doing everything we can help people travel safely during these unprecedented times.
"Clearly, Saturday afternoon's Government announcement and the introduction of a new Tier 4 from midnight tonight led to an unexpected surge in passengers wishing to travel before the further social and travel restrictions are introduced.
"Passengers are reminded they should wear a face covering inside the station and throughout their journey and be mindful and considerate of others travelling."
A spokesperson for Network Rail, which is in charge of the station itself and its concourse, added: “There was an increase in passenger numbers at a few of London’s bigger stations yesterday early evening and a small number of trains were busy. By 10pm passengers levels had returned to normal.”