The UK could have its hottest day ever later this week after temperatures across England exceeded 30C (86F) on Tuesday.
Tuesday's hotspots were published by the Met Office with Cardiff and Watnall, Northampshire at 30C (86F) whilst Frittenden, Kent soared to 32C (89.2F).
Met Office forecaster Luke Miall said temperatures in London are expected to reach 38C (100.4F) on Thursday and which would pass the current record for a day in July which stands at 36.7C (98.1F) recorded at Heathrow Airport in 2015.
He added: "There is now a 40% chance of going over the UK temperature record of 38.5C (101.3F) which was recorded in Faversham, Kent, in August 2003."
Train company Southeastern said it would be running a "significantly reduced service" on Thursday due to speed restrictions announced by Network Rail.
Southeastern operates trains in south east London and Kent but also serves parts of East Sussex.
Mr Miall said: "The coollest areas will be Northern Ireland and western Scotland, although it will still be quite warm it will be in the low 20s rather than the 30s like other areas."
Homeless charity St Mungo's is providing extra support for people who are sleeping rough in the hot weather, including giving out water and sunscreen.
They "urge" anyone concerned about someone sleeping rough to get in touch using the website streetlink.org.uk.
Dr Sam Hampton, a post-doctoral research associate at the Environmental Change Institute, University of Oxford, advised people to wear "lighter, loose fitting clothing before cranking up the air conditioner", adding that: "If necessary, air-conditioners should only be run when all the windows are closed."
A yellow severe weather warning covers most of England, Wales and Scotland until 9am on Wednesday.
The Met Office said there is a "small chance" of damage to property from lightning strikes, hail or strong winds causing potential damage to buildings.
It added there is a small chance driving conditions will be affected by spray, standing water leading to longer journey times by car and bus.