Gocompare have put together a guide to preparing for a flood and protecting your property - https://www.gocompare.com/home-insurance/flooding-and-home-insurance/limiting-flood-risk-and-damage/

In extreme conditions you won't be able to stop flood water, and you should always put personal safety above attempts to protect property and possessions. Despite this, there are steps that you can take to keep water out, to buy yourself time to preserve property and possessions, and to limit the damage that flood water does.