The Competition and Markets Authority (CMA )is investigating the anticipated acquisition by Nationwide Building Society of Virgin Money.
Nationwide’s £2.9bn takeover bid for Virgin Money would create the second-largest mortgage lender in the UK.
The CMA says its investigation will examine whether the move will result in a substantial lessening of competition within any market or markets in the United Kingdom for goods or services.
It will accept comments from interested parties from today until 14 June – and plans to publish an initial decision on 26 July.
The firms had aimed to complete the sale by the end of the year.