The Office of Fair Trading (OFT) is the UK's consumer and competition authority and responsible for regulation and enforcement with regards to mergers and acquisitions.

If the OFT considers that a "substantial lessening" of competition will occur as a result of a merger, it may refer the case to the Competition Commission for further investigation.

The Enterprise Act 2002 empowers the OFT to refer to the Competition Commission completed or proposed mergers for investigation if the business being taken over has a turnover of at least £70 million in the UK, or the merged entity would have a share of at least 25% of supply for particular goods or services in a substantial part of the UK.

The OFT is currently working with the Competition Commission on a joint review of their respective guidelines for substantive merger analysis and assessment.

Further information and details of current and past inquiries are provided on the websites of the OFT and Competition Commission.