Eurostar has blamed the coronavirus pandemic for its decision to remove free wi-fi from standard class carriages, but keep it in the premium seats.
It was responding to a customer tweet which queried the change.
A spokesman told the BBC the move had been temporary and wi-fi had now been restored throughout trains.
He did not explain how Covid-19 had affected providing wi-fi from a track-side network to standard seats.
Mark Jackson, founder of the internet service provider site ISPreview, said the decision to restrict it to premium seats as a result of the pandemic made "about as much sense as dancing naked on lava".
The wi-fi is provided by a track-side network of mobile broadband cells and it was unclear how additional safety measures introduced as a result of coronavirus would impact its delivery to standard seats, he added.
Eurostar said in a statement: "Following an unprecedented fall in demand across the travel industry, we made some temporary changes to simplify our business. This included the wi-fi connectivity offered on board.
"We are pleased to say that wi-fi is now available on board and is free throughout all classes of service."