Japan's Nikkei business daily reported that Hitachi had decided to freeze the project, although it also reported that the board had yet to vote to make it a formal decision.
A spokeswoman for British Prime Minister Theresa May said talks with Hitachi were continuing.
"On Hitachi, the negotiations on that are ongoing and those are obviously commercially sensitive so I can't comment," the government spokeswoman told reporters when asked about the reports.
May met Japanese Prime minister Shinzo Abe this week in London. He told her Japan did not want to see a disorderly Brexit when Britain leaves the European Union in March.
Hitachi said in Friday's statement that it had been assessing the project "including its potential suspension and related financial impact."
"Should any matter arise which needs to be disclosed Hitachi will announce information in a timely manner," Hitachi said.
Nikkei reported that Hitachi had decided to freeze the project, leading to a special loss of 200 billion to 300 billion yen ($1.9 billion to $2.8 billion) for the year ending in March. Hitachi's board would vote on the suspension at a meeting next week, it reported without citing its sources.
In Friday's statement, Hitachi said: "These articles aren't based on Hitachi's decision or disclosed information."