Anti-terror marshals will be deployed to protect London Underground from attacks like last week's bomb blasts in Spain, a Sunday newspaper reports.

The plain clothes officers, part of British Transport Police, will carry equipment on Tube trains to test for nuclear, biological and chemical (NBC) weapons, according to The Observer.

The move follows the tragic deaths of nearly 200 people in Madrid when 10 bombs were exploded simultaneously on trains near stations around the Spanish capital.

While it is still unclear who planted the bombs, al Qaeda has been named as a strong suspect.

London's Tube has long been considered a possible target for attack, and terror drills were carried out at one station last year to establish how far emergency services were able to protect the network and civilians.

A transport minister said at the time more work was needed to be done.

Sky marshals were introduced on some flights from London earlier this year. Pilots fought to ensure they would retain overall control of passenger aircraft despite the presence of guards on flights.