A dream Caribbean cruise turned into a disaster for 1,600 passengers in September, when the Oriana spent three weeks on a magical mystery tour of cancelled island itineraries.
Holiday makers allege P&O's marketing people blithely ignored concerns of shipping staff and sent the Oriana into the Bahamas' worst hurricane season for 60 years.
Action group leaders were due to receive written counsel's opinion this weekend, confirming P&O has a case to answer.
Preston-based solicitors Paul Watson & Co then plan to write to between 400 and 500 protesting passengers, before going ahead with a class action, which could cost P&O up to pounds 5m, before costs, damages and knock-on effects of bad publicity.
The moves come just days after rival Cunard, owned by Trafalgar House, finally agreed to pay out pounds 7.5m after a trip on the QE2 last December turned into a "cruise from hell".
Amid stories of exploding toilets after a bodged refit, Cunard's intransigence made it a laughing stock for much of this year.
However, P&O insists it has nothing to learn from Cunard's experience and has refused to set a precedent with a payout offer.
"We still wish to know who's making what claim. We're waiting for a response. We'd be surprised if they issued a writ at this stage," said Gwynne Hughes, managing director of P&O Cruises.
Trouble started soon after the luxury liner left Southampton on 1 September. "We hit Hurricane Iris in the Atlantic a few days out," said Sue Mills, who heads the southern section of the action group.
"You either got drunk or got scared. The waves raged 13 decks up with spray and that was before the storm got bad."
Oriana had to outrun Hurricanes Lewis and Marilyn, cancelling stops in Barbados, Bermuda, Grenada and St Lucia. When it finally put in St Vincent after 10 days, it was Sunday and the island, one of the poorest, was practically closed.
In the meantime, "all we saw were container ships and one bird," one passenger said.
So far, P&O has only offered a 20 per cent discount on any future cruise - an offer made after a near mutiny on board in Madeira.
Mr Hughes said the booking conditions stated that P&O was not liable for bad weather.