(Reuters) — Britain’s biggest pubs group, Stonegate, which is suing three insurers for £1 billion ($1.2 billion) over lockdown losses, battled the COVID-19 pandemic “day by day, venue by venue,” a London court heard Monday.

Ben Lynch, a lawyer for Stonegate, said the company's 760 insured pubs, bars and nightclubs at the center of the case had each faced separate challenges, opening and shutting at differing times according to regional rules — and seeing business drop by up to 90% below projections.

If successful, the Stonegate case could give fresh momentum to a second wave of claims against insurers that might cost the industry billions of pounds, further damage reputations and push premiums even higher for businesses and consumers, experts say.

Stonegate is suing Zurich Insurance, Liberty Mutual and MS Amlin, alleging the pandemic, government-ordered closures and restrictions triggered business interruption cover multiple times and that the interruption and interference will continue until April 2023.

Insurers accept Stonegate's businesses were covered by their policies but contend that cover was limited to one business interruption payment of £2.5 million, which has been paid, court documents show.

In total the insurers have paid £14.5 million, including £12 million for additional increased costs of working, and say their liability is limited to £17.5 million. They label the claim “hugely overstated,” filings show.

The case is by far the largest since the U.K. Supreme Court ruled last year that many insurers had wrongly rejected business interruption claims from thousands of small businesses that had to close or restrict trading to curb the coronavirus.

Policyholders have so far received nearly £1.35 billion in compensation. But not all policy wordings were covered and, where they were, some dispute payout levels.

Insurers have been on notice since Corbin & King, the owner of London's Wolseley restaurant, won a similar BI case against insurer Axa in February.

Multi-million-pound claims by sandwich and pasty chain Greggs against Zurich and Strada and Coppa Club owner Various Eateries against Allianz will be heard next month.