## Facts

- The case concerned a merger involving bus services in South Yorkshire.
- The Monopolies and Mergers Commission (MMC) reviewed the merger under the Fair Trading Act 1973, which covers mergers affecting a "substantial part of the United Kingdom."
- South Yorkshire, despite being small in land area, was a key market for bus operations due to the concentration of bus routes and their impact on local transportation.
- The MMC asserted that South Yorkshire represented a "substantial part" of the UK for the relevant market.
- The House of Lords was called upon to interpret whether the MMC’s intervention was valid given the area's small geographic size.

## Issues

1. Whether "substantial part of the United Kingdom" in the Fair Trading Act 1973 should be interpreted by reference to economic significance or solely by geographic and population size.
2. Whether the MMC could lawfully intervene in a merger situated in a geographically small but economically significant area.
3. What factors should determine the boundaries of the relevant market in merger reviews.

## Decision

- The House of Lords ruled that "substantial part" concerns the economic importance of the area, not its land area or population.
- It held that a smaller region could qualify as a "substantial part" if it has significant economic activity, while a physically larger area might not if it lacks such importance.
- The Court upheld the MMC’s authority to review and intervene in mergers where the affected area, though small, plays a significant economic role in the relevant market.

## Legal Principles

- "Substantial part of the United Kingdom" under the Fair Trading Act 1973 is determined by the significance of the area in economic terms, not by size or population alone.
- The "economic function" test requires authorities to assess the merger’s impact on competition, considering factors such as volume of trade, role in the national sector, and local business presence.
- Defining a relevant market may involve geographic, product, or service boundaries, always focusing on economic activity and competition risks rather than mere physical dimensions.

## Conclusion

The House of Lords in R v Monopolies and Mergers Commission, Ex parte South Yorkshire Transport Ltd established that the assessment of a "substantial part" for UK merger reviews is based on economic significance and function rather than physical size, providing enduring guidance for competition law and regulatory authorities.

R v Monopolies and Mergers Commission, Ex parte South Yorkshire Transport Ltd [1993] 1 WLR 23