“Exceptional, perhaps record high, temperatures are likely on Monday and Tuesday. The nights are also likely to be unusually hot for the UK to be, especially in urban areas. This is likely to have far-reaching consequences for people and infrastructure. ” writes Met Office.
They also write that temperatures are expected to fall again from Wednesday.
Red warning means “severe or prolonged heat wave” where illness and death can occur among people who are healthy and in good shape. People are asked to be aware of signs of heat-related ailments.
It is UK Health Security Agency (UKHSA) which determines the levels and what they entail. Red, which is level 4, is considered a “national emergency”.