Parts of the country are bracing for flooding and major incidents have already taken place with rail services disrupted on the Northern network after tracks flooded.
More than 120mm of rain has already fallen in parts of the country, with 123.4mm at Honister Pass in Cumbria in the 24 hours up to 6am on Wednesday.
Nearby Seathwaite saw the second highest total, with 107.2mm, and some isolated spots could see up to 200mm, the Met Office said.
Fifty-one warnings have been issued by the Environment Agency across England, with 179 less severe flood alerts, mainly across the Midlands and north of the country.
Speaking during Prime Minister’s Questions, Boris Johnson told MPs: “Our sympathies also go out to those affected by the latest floods.
“I want to thank the Environment Agency and our emergency services for the work they’re doing to support those communities, and I’ll be chairing a Cobra meeting later on to co-ordinate the national response.”
Almost the whole of England, Wales, and Northern Ireland are subject to yellow weather warnings for rain until midday on Thursday, with a more serious amber warning stretching from the East Midlands to the Lake District.
The amber alert warns of the risk of flooding and deep floodwaters which could pose a risk to life, and there are further yellow warnings for snow and ice in Scotland.
Met Office forecaster Grahame Madge described Christoph as “quite a slow-moving system” which is bringing “a variety of weather” to the UK.
The meteorologist said: “While rain remains the main hazard in the south, further north we’ve got snow and ice remaining a risk.
“The system will work its way through, we are expecting significant totals of rainfall and when you combine that with snowmelt it can lead to localised flooding across the affected regions.”
The force said people should leave flooded homes if instructed, despite the stay-at-home messaging of the pandemic.
Assistant Chief Constable Nick Bailey said: “Coronavirus remains a threat to everyone’s health and people should not leave their homes unless it is absolutely essential, but where there is a risk of flooding, that is clearly essential and we’re working with our partners to ensure that people can do this as safely as possible.”