Greater Manchester Police say the plot could have been "the deadliest terrorist attack in UK history".
The government has now said it will lift the intended threshold from £1m to £2.5m.
Ex-councillor Philip Young is one of six men accused of more than 60 offences against Joanne Young.
One couple say they had decorated the boat for Christmas but would now spend it in a hotel.
The Met Office says that 2025 is likely to be the UK's hottest year since records began.