The public have been urged to avoid travelling as record-breaking temperatures are predicted to hit the capital next week.
Record-breaking temperatures as high as 41C could occur around London early next week, and the Met Office chief executive Penny Endersby warned of “absolutely unprecedented” conditions.
Cabinet Office Minister Kit Malthouse said transport services face “significant disruption” as he urged people not to travel.
Ministers held an emergency Cobra meeting on Saturday after experts warned that lives could be at risk due to the scorching temperatures.
After chairing the meeting, Mr Malthouse told the BBC: “Obviously the transport providers are messaging people that they should only travel if they really need to on Monday and Tuesday.
“Services are going to be significantly affected. The heat will affect rails, for example, so the trains have to run slower. There may be fewer services. People need to be on their guard for disruption.
“If they don’t have to travel, this may be a moment to work from home.”
Mr Malthouse said steps have been taken to ensure hospitals and ambulances that may come under pressure were prepared, while schools were being issued with guidance to enable them to remain open.
He added in a separate statement: “It’s important that we all continue to follow public health advice to keep cool, and take simple precautions like drinking lots of water and seeking shade, and also checking on vulnerable friends and neighbours.”
Saturday kick-started the beginning of the heatwave, with Heathrow Airport and Kew Gardens recording the highest temperatures at 29.1C.
The warm weather saw increased demand for water in some parts, with South East water confirming residents in Challock and Molash, in Kent, had no water due to “continuous hot weather and significantly increased demand for water” putting “significant pressure on our network”.
A statement from the supplier said: “We’re continuing to work on restoring your supplies, and will continue to work on this overnight.
“As a precaution, we’re going to open up the bottled water station at Challock Village Hall tomorrow morning, at 8am.
“The team will be there until 7pm tomorrow night.”
Meteorologists say there is an 80 per cent chance the mercury next week will surpass the previous record temperature of 38.7C set in Cambridge in 2019.
Scorching temperatures are predicted on Monday with Peterborough expected to hit 37C and Milton Keynes, Norwich and Lincoln thought to hit 36C.
Temperatures are forecast to increase by several more degrees on Tuesday – up to the mid-30s for much of England and Wales.
There is a 50 per cent chance of temperatures reaching 40C somewhere in the UK that day, likely along the A1 corridor which runs from London to Scotland through counties including Lincolnshire, Nottinghamshire, Yorkshire and the North East.
Following the issuing of the Met Office’s first red warning for extreme heat, covering a swathe of England from London to Manchester and York on Monday and Tuesday, its chief executive Penny Endersby said people can find it hard to to know what to expect when “climate change has driven such unprecedented severe weather events”.
“Here in the UK we’re used to treating a hot spell as a chance to go and play in the sun,” she added.
“This is not that sort of weather.”
The amber warning initially covers all of England on Sunday and extends to southern Scotland and Wales from Monday until Tuesday.
London Mayor Sadiq Khan held a special meeting with key senior officials from agencies including the NHS, the Met Police, London Fire Brigade, London Ambulance Service, councils and Transport for London on Friday to ensure there is a robust plan in place to deal with the level four heat alert.
Mr Khan has urged Londoners to undertake only essential travel on Monday and Tuesday and to prepare for disruption because speed restrictions will be in place on rail and Tube networks.
A high air pollution alert for London has also been issued by the mayor for Monday.