Defibrillator-carrying drones promise to dramatically boost survival rates for people suffering cardiac arrest after a new study found they could reach patients four times faster than an ambulance.

The fully automated eight-rota machines can fly, unimpeded by traffic at up to 50mph and deliver an easy-to-use heart-starting kit to critically ill patients.

The technology should enable more NHS emergency units to meet the eight-minute response target for the most urgent cases, which has slipped badly in recent years.