LONDON (REUTERS) - British Prime Minister Boris Johnson's chief adviser on the union, Luke Graham, has departed after a dispute inside Downing Street over the UK government's strategy to counter growing calls for Scottish independence, the Financial Times reported on Wednesday (Feb 3).

Oliver Lewis, an adviser to Johnson, will lead the union after Graham's departure, the FT said, citing government officials.

Graham was unhappy with both his role and No. 10's strategy for the union, the report added, citing officials with knowledge of the dispute. The unit was created to help efforts to keep Scotland within the UK.

Graham will move to Scotland to assist the Scottish Conservative Party's campaign for May's Holyrood elections, the FT said.

Graham's departure comes after Johnson's visit to Scotland last week where he said Scottish nationalists should stop talking endlessly about another independence referendum as the 2014 vote was a once-in-a-generation event.

The UK government declined to comment.