Boris Johnson has sought to reassure people about the safety of the Oxford/AstraZeneca Covid vaccine as a trial in children was paused while regulators investigate rare reports of blood clots, largely in younger women.

The prime minister urged the public to take the jab when it is offered, while scientists stressed the side-effects were extremely rare and the benefits of protection against coronavirus were great.

Some UK drug safety experts believe there could be a causal link between the AstraZeneca jab and rare blood clotting events including cerebral venous sinus thrombosis (CVST).

But they said vaccination programmes must continue, with risk mitigation for women under 55. Doctors have already been alerted to CVST symptoms, which include headache, blurred vision and fainting.