A British train company that compared its service to the cooking chocolate of a discount retailer in a tweet has been threatened with legal action.

The spat on social media erupted after a disgruntled passenger named Kevin tweeted an image of a departures board showing cancelled trains, and wrote sarcastically: "Why, Ambassador @TLRailUK, with this fine service you are really spoiling us."

Thameslink replied: "Very sorry Kevin. Appreciate at the moment the service is less Ferrero Rocher and more Poundland cooking chocolate."

Poundland retail director Austin Cooke issued a response to Charles Horton, chief executive of Thameslink's parent company Govia Thameslink Railway (GTR), describing the train operator as "off the rails".

Mr Cooke wrote: "Aside from the breach of our trademark, we think you're taking the chocolate biscuit."

He said GTR has "no right to use our name to describe poor service", stating that the budget chain served eight million shoppers last week and has a "pretty good idea about what great customer service is".

"But if we ever fall short, perhaps we'll describe ourselves as a bit Thameslink," he continued.

"If you don't want to hear from our extremely twitchy legal team, we suggest you remove your tweet."

.@TLRailUK You’re ‘off the rails’ #TLFail #Proudland pic.twitter.com/rago9G1zmh

— Poundland (@Poundland) May 30, 2018

Thameslink deleted its original message and tweeted: "Very sorry team for using your name here. I have removed the offending tweet."