The Government has sent a further 200 troops to help the rescue efforts in flood-stricken northern England.
Some 300 military personnel have already been mobilised to help communities in Yorkshire and Lancashire struggling to tackle the flooding caused by "unprecedented" levels or rain in recent days.
Rivers in York, Leeds and Manchester have burst their banks, leaving properties under water and causing hundreds of people to be evacuated from their homes just days after Christmas.
The Government has vowed to review flood defences as the Army was mobilised this morning to help emergency services carry out mass evacuations.
David Cameron chaired a meeting of the Government's emergency Cobra committee on Sunday, discussing the catastrophe with cabinet ministers, military and transport bosses, emergency services leaders and the Environment Agency.
A Number 10 spokesman said: "The Prime Minister praised the work of the emergency services in dealing with this unprecedented event, but recognised this was an incredibly serious situation which had led to some very serious flooding.
"The decision was taken to deploy additional military personnel to ensure those affected by the flooding have the support they need, with 200 personnel being deployed to flood affected areas, alongside the existing 300 already there.
"A further 1,000 military personnel are being held in reserve should the situation worsen."
Emergency financial assistance will also be put in place for affected areas, and homes and businesses damaged by flooding will have access to the same package of support announced for those affected by Storm Desmond.