The Met Office issues alerts and warnings during hot weather when the risk of certain 'threshold temperatures' being reached increases or when those temperatures are reached.
The threshold temperatures vary across the UK from 28C in the north east to 32C in London.
- Level 1 - The minimum state of vigilance during the summer, with general preparedness and long-term planning for authorities.
- Level 2 - Heatwave warning. Social and healthcare services will be working to ensure readiness and swift action to reduce harm from a potential heatwave.
- Level 3 - Heatwave. requires social and healthcare services to fulfil specific actions for high-risk groups and is triggered when threshold temperatures have been reached.
- Level 4 - National emergency. Reached when a heatwave is so severe or prolonged its effects extend outside the health and social care system and illness and death may occur among the fit and healthy, and not just in high-risk groups.
- See the full threshold temperatures for each region here.
The south east and London are currently at level three with the majority of the rest of the country at level 2 or 1.