Police were facing serious questions last night over how the knife-wielding terrorist was able to enter the Parliamentary estate.

There were unverified claims that no armed officers had been on duty at the main Carriage Gates, facing Parliament Square, which the Prime Minister uses to enter the House of Commons.

They are also used by other MPs, staff and visitors. At least four staff are usually stationed at the gates, two outside and two inside.

Police were facing serious questions last night over how the knife-wielding terrorist was able to enter the Parliamentary estate

Parliament Square, usually populated by thousands of visitors and people who work in the corridors of power, was today abandoned after police put the area on lockdown

The entrance is also blocked by metal barricades and barriers. Although armed guards routinely patrol the grounds, they are not stationed permanently at a fixed position at the main gate. It is understood the officers work a ‘fluid’ patrol pattern so potential terrorists do not know where they are located.

Labour MP Mary Creagh urged the authorities to step up security following the atrocity.

‘The one weak spot on our estate is those Carriage Gates,’ she said. ‘We have four police officers there. Two on the gate going in, two on the gate going out. We see them every day, we’re friends with lots of them.

‘I think we will need to look at security at the Palace in the wake of this incident but this is a plan for another day. It’s a terrible, terrible day for Parliament.’

Colonel Richard Kemp, former commander of UK forces and a security expert, said: ‘He shouldn’t have been able to get in and this shows there must have been a lapse in security with big consequences. People will have questions to answer.

‘It is such a high profile target and they should consider there is permanent coverage of armed police at the main gates.

DONALD TRUMP JR ACCUSED OF 'CRASS' TWEET TO SADIQ KHAN Donald Trump’s son was accused of insensitivity after he attacked London Mayor Sadiq Khan on Twitter Donald Trump’s son was accused of insensitivity after he attacked London Mayor Sadiq Khan for claiming the terror threat was ‘part and parcel of living in a big city’. Donald Trump Jr linked his tweet to a report of the mayor’s remarks last September with the comment: ‘You’ve got to be kidding me?!’ Mr Trump’s remark came within hours of yesterday’s attack in London and was unaccompanied by any expression of sympathy or condemnation. One Twitter user said: ‘As a Londoner, I would like to politely request you desist from such crass tweets at a time like this.’ President Trump yesterday phoned Theresa May to offer her the full co-operation and support of the United States. Donald Trump Jr linked his tweet to a report of the mayor’s remarks last September with the comment: ‘You’ve got to be kidding me?!’ Advertisement

‘This should not have happened. There’s been an element of complacency because the security services have been so effective. Lessons have to be learnt.’

A House of Commons spokesman said last night: ‘The security of Parliament is our highest priority, and therefore we cannot comment on the details of this ongoing incident.’

ATTACK THAT POINTS THE FINGER STRAIGHT AT ISLAMIC STATE Islamic State was last night top of the list of groups thought to be behind the Westminster attack. As security experts said the brutality of the crime pointed towards the terrorists, IS supporters posted gloating messages online. On private messaging app Telegram, one user shared pictures of the attacker’s route. Another post features a mocked-up image of the Elizabeth Tower on fire with the message: ‘Soon. Our battle upon your land. Not started yet. Be upon you. Only waiting.’ According to Ahmet Yayla, senior research fellow at the International Centre for the Study of Violent Extremism, the messages were shared on a ‘credible’ IS channel. Last night security experts said the attack had the hallmarks of IS. A source added: ‘It would be a fair assessment because of the methodology used – driving vehicles into people in a horrible random attack in a crowded place.’ Just before Christmas, IS released a manual which instructed jihadis to plough a lorry into an outdoor market and inflict a ‘bloodbath’. The terror group’s Rumiyah magazine said using a vehicle was the most successful in ‘harvesting’ large numbers of non-believers. It said the tactic was ‘superbly demonstrated’ in Nice when 86 people were massacred by a lorry on Bastille Day last July. Then in December, a lorry plouged through a Christmas market in Berlin, killing 12 and injuring nearly 50. Advertisement

The Parliamentary Security Department is responsible for security for both Houses and works alongside the Metropolitan Police Service, which provides armed and unarmed policing. Civilian security officers on the site were, until last year, employed by the Met but are now Parliamentary employees. They often have the job of letting cars in and out of the gate, it is understood.

The Prime Minister last night chaired a 45-minute meeting of the Cobra emergency committee to plot the immediate response to the attack.

Theresa May brought together Government ministers, police officers, security agencies and London Mayor Sadiq Khan. The session in Whitehall was addressed by Acting Met Deputy Commissioner Mark Rowley, Britain’s most senior anti-terror police officer.

Home Secretary Amber Rudd, who had been on a visit to Pakistan to discuss counter-terror, cut short her trip and was returning home last night.

Mr Rowley said: ‘The people of London will see extra police officers – both armed and unarmed – out on our streets. We can call on the support of the military should we need to at a future point.’

It is understood that security is being stepped up at rail terminals. Senior figures have repeatedly warned the UK remains a major target. The official threat level is ‘severe’ – meaning an attack is ‘highly likely’.

It was revealed this month that 13 potential attacks have been thwarted in Britain since the murder of Lee Rigby in 2013, while counter-terrorism units are running more than 500 live investigations. Experts have warned of the threat posed by extremists carrying out unsophisticated but deadly attacks using knives or vehicles as weapons.

A recent study found the proportion of plots in the UK involving knives has soared from 4 per cent to 44 per cent.

Baroness Pauline Neville-Jones, a former chairman of the Joint Intelligence Committee, said: ‘It is the kind of terrorist incident that’s very hard to deal with because, as we now know, this is the kind of incident that can be mounted without necessarily leaving any kind of trail which the police and security services and intelligence services can actually pick up to prevent it.’