The merger was recommended by the government as part of plans to improve the UK competition regime.
"The new Competition and Markets Authority (CMA) must be proactive and focus on achieving real change in markets where there is consumer harm," said chief executive James Lowman. "Our experience of scrutiny in the grocery market is authorities constrained by a limited view of consumer harm. This can be rectified by empowering the new CMA to act in the broad 'public interest'."
Lowman urged the government not to make the same mistakes as they did with the grocery market inquiry. "There must not be a repeat of the experiences of the grocery inquiry where the Commission found harms and recommended remedies that remain unimplemented three years on."
A decision on the merger is expected in September.