The extreme heat weather warning system ranges from yellow to red and indicates how likely and how much of an impact the weather will have on public life.
An amber warning states that temperatures are likely to have a high impact.
Network Rail has warned speed restrictions are likely to be in place this week on some parts of the network most affected by the hot weather.
It adds that this helps because slower trains exert less force on the track and reduce the likelihood of buckling, avoiding the major disruption caused by a buckled rail.
Fire services have also urged people to have picnics instead of barbecues during the warm weather after a spate of grass fires.
Meanwhile The AA Driving School and RAC have said motorists should carry water with them, start their journeys earlier in the day, plan their routes and check their vehicles before setting off on any journeys.
The whole of England is largely expected to experience sunny days with some cloud over the next week to match the temperatures of mid to high 20s.
It will cool off a little on Friday, with the north-west and north-east of England predicted to have some rain with temperatures reaching highs of 19°C, ahead of a warmer weekend.
Temperatures are then expected to spike to 32°C on Sunday and in excess of 35°C in the southeast.
Scotland and Northern Ireland are predicted to have a cloudier week ahead, with rain forecast for Tuesday and Friday.
Clouds with sunny spells could be widespread across the two areas for the rest of the week, with temperatures remaining in the mid to high teens throughout the week.
They will also benefit from the scorching weekend temperatures ahead alongside some cloud, with highs of 22°C predicted in Glasgow and Belfast.
Weather forecasting models suggest it is possible – though not likely – temperatures could reach 40°C in the UK next weekend, which would break the current British temperature record of 38.7°C, set in Cambridge in July 2019.
However, a spokeswoman for the Met Office said it takes computer modelling into consideration when making its predictions, and it believes the warmest weather will not reach 40°C.
A Level Three Heat Health Alert has also been issued by the Met Office and UK Health Security Agency (UKHSA) from 9.00am on Monday to 9.00am on Friday in the east and south east of England, with the rest of the nation having a level 2 alert in place.
The four-level system highlights the potential health impacts of these high temperatures.
