Counter terrorism officers are tonight leading the investigation into the murder of Tory MP Sir David Amess, as forces across the country are being urged to launch an ‘immediate review’ of security for politicians.

It comes after horrified onlookers screamed for help as they tried to save the Conservative MP who was brutally stabbed to death in front of them at his Southend constituency surgery.

The popular politician – who won at the last general election with a margin of 14,000 votes – was knifed ‘multiple times’ by a 25-year-old killer – believed to be of a British national of Somali heritage.

It is understood the killer booked an appointment to see the MP before stabbing him to death at his constituency surgery, according to the Sun.