THE NATIONAL threat level raised from ‘severe’ to ‘critical’ yesterday after a horrific homemade bomb attack on the London Underground.

An explosion on the District Line near Parsons Green saw more than 20 people receive serious burn injuries during the morning rush hour.

Police are yet to hunt down the bomber and the national terror threat level has been raised as a result of yesterday’s attack.

Thames Valley Police has warned it will be stepping up its resources in busy areas across its forcing areas.

A post on the force’s website reads: “This means an attack is expected imminently and you may see increased policing and security presence across Thames Valley in key sites and public places to provide reassurance.

“We urge the public to be vigilant and to report any suspicious activity by calling the Anti-Terrorism Hotline on 0800 789321 or 999 in an emergency.”