Britain’s biggest drugmaker, AstraZeneca, is understood to be in discussions to take over its US rival Bristol Myers Squibb in a deal that would create a near-$400bn (£300bn) pharmaceutical group.

AstraZeneca, run by Pascal Soriot, its longtime chief executive, is the second-biggest listed company in the UK, with a market value of nearly £196bn before the news broke. BMS, headquartered in Princeton and known for its cancer treatments, is worth $133bn.