The company admitted it had not met a pledge to eradicate these old-fashioned “hopper” toilets by 2020.

The promise had been made in 2017 by Mark Carne, formerly Network Rail's chief executive, who said the problematic toilets would be swapped for retention tanks that could be emptied at stations instead of discarding sewage onto the tracks.

This would be achieved by the end of decade, he claimed.

Mr Carne said of hopper toilets at the time: “It’s disgusting. I’ve been out there with the track workers and you see it coming, like a plume of steam.  

“It’s totally unacceptable and I’m pleased we’ve got government agreement.”

However, this pledge has not been met, EMR, which took over the franchise from East Midlands Trains in 2019, confirmed to LeicestershireLive.

A spokesperson stressed that the “vast majority” of trains had already been fitted with Controlled Emissions Toilets.

The new aim is to upgrade all train toilets by 2023, as per Network Rail’s updated targets.

“Prior to the Covid pandemic, we were due to remove all of our Intercity trains without Controlled Emissions Toilets by the end of this year,” the spokesperson said.

”Although we will be reducing the number of these trains in service next month, their complete removal will now be delayed until May 2021 as part of a wider timetable enhancement for services to and from London St Pancras.

“This is part of our multi-million-pound investment plan which includes the complete replacement of our train fleet with either brand new or fully refurbished trains.”

Footage of the group, known as TPD TV, leaving their waste on a layby caused outrage among locals, and the incident was logged with Police Scotland, Highland Council, Sepa and the NC500 organisation, reported The National.

The group originally stated that the video had been taken “out of context” and said: “Whilst we understand the concerns, please bear in mind that we are an entertainment channel. Not everything is real. We hope our dedicated viewers continue to enjoy our content.”

However, an apology has since been issued in response to increasing backlash from locals.