Armed police are being told to shoot terrorists through the windscreens of cars and lorries used in Westminster-style attacks.

Officers were previously instructed not to shoot drivers of moving vehicles because of the dangers posed to nearby pedestrians and road users.

But Simon Chesterman, the National Police Chiefs' Council lead on armed policing, said: "As often happens the terrorists keep adapting their tactics. We have seen some horrible and different tactics lately using vehicles and lorries.

"It used to be that within our policy we used to talk about not shooting a moving vehicle, that was because of the danger we might cause if we fired at a driver then clearly we might cause a real problem with the vehicle.

"But if the vehicle is being used as a weapon in the first place there aren't many tactics available in relation to stopping it, especially if it is a very large lorry.

"So driving a vehicle in front of it for example is not going to stop it so you need to shoot the driver."

The new policy comes after Khalid Masood killed four people on London's Westminster Bridge when he mounted the pavement in a car and ploughed into pedestrians.

The attack last month led to questions over how future terror incidents involving vehicles could be stopped in cities like London.

Chesterman said as well as the new training, armed officers will be given high powered .556 calibre ammunition capable of penetrating glass and body armour to prevent bullets deflecting off vehicles.

"What tends to happen is that when a bullet hits glass, it will deflect it, so shooting through glass is difficult," he said.

But he added: "I'm confident that our armed response vehicle officers are equipped with the right weaponry and ammunition to stop a lorry."

Chesterman said police forces across the UK are recruiting thousands of new armed officers as part of the response to large-scale terror attacks, such as those carried out in Paris and Mumbai in recent years.

The number of firearms officers is set to rise to about 10,500 by next year – the same level as 2010.

Chesterman said the capability of armed officers was "phenomenally different" from previous years following investment in recruitment and training.