Britain is facing Christmas strike chaos as militant unions have announced walk-outs at the Post Office and on one of the country's busiest railway lines.

Cards and parcels could be delayed after staff at the UK’s 300 largest Post Offices - which handle 20 per cent of all post - announced a five-day strike which will last until Christmas Eve.

It is the longest continuous strike in the 300-year history of the Post Office and comes as rail workers on one of the country’s busiest commuter lines begin a series of crippling strikes.