Ministers have been warned that the chemicals used to treat water may run short if Britain leaves the EU without a deal

The international development secretary sought to reassure bemused cabinet colleagues yesterday that Britain would not run out of clean water in the event of a no-deal Brexit because it could learn from its experience helping poverty-stricken third world countries.

Penny Mordaunt, a Brexiteer, insisted there were very easy ways to purify water, which is necessary to prevent outbreaks of cholera and other water-borne diseases, if the UK left the EU without a trade agreement in place.

Her colleagues were alarmed at the suggestion that Britain would have to rely on processes usually seen in the poorest parts of the world. “I don’t remember that being written on the side of a bus,” one minister said. “I sat there thinking ‘Has it really come to