The Competition and Markets Authority has fined ComparetheMarket £17.9m for breaching competition law.
The regulator’s investigation concluded that the comparison website had imposed wide “most favoured nation” clauses on providers selling home insurance.
The breaches took place between December 2015 and December 2017.
Michael Grenfell, the CMA’s executive director for enforcement, said: “Price comparison websites are excellent for consumers. They promote competition between providers, offer choice for customers, and make it easier for consumers to find the best bargains.”