Irish Rail bills itself as part of a solution to the climate crisis and pollution, saying clean transport can help avert global warming, rising sea levels and famine.

But don’t try using your own reusable coffee cup on one of its trains. Ireland’s national railway network has banned passengers from using their own cups, citing safety concerns.

“The reasons that we cannot permit [reusable cups] is because all sizes do not fit under the spout and also closing mechanisms can vary,” the company tweeted on Monday. Different sized cups, it said, could lead to catering staff being burned.

The statement followed complaints from passengers that Irish Rail staff did fill reusable cups but only after first pouring the tea or coffee into disposable cups, which were then discarded, a story first reported by the Irish Times.

“I watched incredulously one morning as the assistant made a coffee in the disposable cup, poured it into my reusable one and then binned the disposable cup. It’s beyond barmy,” tweeted Calvin Jones.

They can't fit any "normal" size reusable cups under their hot water tap on the catering trolley. I watched incredulously one morning as the assistant made a coffee in the disposable cup, poured it into my reusable one and then binned the disposable cup. It's beyond barmy. — Calvin Jones (@WriterCJ) December 16, 2019

Another passenger tweeted: “They literally took my money, filled up my cup with tea and then threw the paper cup in the bin UNUSED.....I give up.”

The company said the Belfast to Dublin route is trialling direct pouring into a reusable cup – as long as it’s one of the company’s branded cups sold onboard.

Irish Rail also said it had moved to 100% recyclable cups but, challenged on Twitter, conceded that such cups tended to not actually be recycled. “It is not that we don’t bother recycling them. It’s that they are currently not widely recycled in Ireland.”

Peter Kavanagh, a Green party councillor in Dublin, scorned the policy. “Our cups are 100% recyclable, but not in this country and we won’t be recycling them. We just throw them in the rubbish. Please congratulate us now.”