A rail firm that compared its poor service to chocolate from Poundland has been threatened with legal action by the discount chain.
Thameslink has apologised after making the comment in reply to a passenger who was angry over train cancellations.
In response, Poundland retail director Austin Cooke said it had "no right to use our name to describe poor service".
It comes after more than 450 Govia Thameslink Railway trains were either cancelled or ran late on Wednesday.
Thameslink had responded to a tweet from a passenger, called Kevin, who posted a picture of a departure board showing train cancellations.
In response, Thameslink replied: "Very sorry Kevin. Appreciate at the moment the service is less Ferrero Rocher and more Poundland cooking chocolate."
It prompted Mr Cooke to tweet Charles Horton, chief executive of Thameslink's parent firm Govia Thameslink Railway (GTR), stating that Poundland served eight million shoppers last week and has a "pretty good idea about what great customer service is".
Mr Cooke added: "But if we ever fall short, perhaps we'll describe ourselves as a bit ThamesLink.
"If you don't want to hear from our extremely twitchy legal team, we suggest you remove your tweet."
GTR later apologised to Mr Cooke and deleted their earlier tweet.
It has been dogged by disrupted services since the publication of new timetables on 20 May.
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Very sorry team for using your name here. I have removed the offending Tweet. ^Neil— Thameslink (@TLRailUK) May 30, 2018
Its poor performance, along with that of Northern rail, prompted Transport Secretary Chris Grayling on Wednesday to say the "rail industry has collectively failed" passengers.
GTR said it expected disruption to ease "over the coming month", while Northern said it had commissioned a report to "ensure lessons are learned".
Mr Grayling said: "The way timetabling is done has to change."
GTR runs Thameslink, Southern, Great Northern and the Gatwick Express, while Northern runs services across North of England from Newcastle to Nottingham and in Greater Manchester, Yorkshire, Cumbria and Merseyside.
Many services across the country suffered 'Meltdown Monday' after rail changes when the new timetables came into force.