Investigators have a working theory on how the Salisbury nerve agent was administered

A delegation from the international body asked to independently verify British claims on the use of a Russian nerve agent in the Salisbury poisoning will not arrive until Tuesday, almost a week after it was asked.

Britain’s leading expert on chemical weapons said that the chances of inspectors from the Organisation for the Prohibition of Chemical Weapons finding traces of novichok at the crime scene were decreasing “by the day” as it degraded.

Samples of blood taken from the victims should allow the agency to test claims that novichok was used, Alistair Hay, a scientist who sits on one of its boards, said.

Officials in London acknowledge that there has been a delay in arranging access for the inspectors. They hinted at opposition from within