A warm front stretching south-east from East Anglia to Kent means areas inside this zone are likely to see warm ‘sticky’ weather, a Met Office forecaster has said.
Regions further north will enjoy much cooler climes, with a few showers over Scotland and Northern Ireland.
The record from Monday was 29.7C, which was reached in Teddington in Middlesex.
Met Office forecaster Simon Partridge said there is a ‘reasonable chance’ Wednesday’s warmest temperature could be higher.
He said: ‘It’s going to be pretty close and there’s a reasonable chance that we will just pip it.
‘There’s a good chance that we could see 30C temperatures just north of London and a small chance of seeing 31C.
‘The heat will be very much concentrated in the south-east corner of the UK, with a cold front across more northern areas.
‘As well as being very hot it will become increasingly humid, so it’s going to feel really quite sticky and muggy by the early evening.’
Mr Partridge added that most football fans in Wales can look forward to dry, cloudy weather and evening temperatures of around 15C as the country takes on Turkey in the Euros at 5pm.
However, the outlook for fans watching in east Wales and England could be very different, with a yellow weather warning for thunderstorms in place from 6pm on Wednesday lasting throughout Thursday until midnight.
The Met Office has also issued yellow warnings for storms which could cause flooding and power cuts in south-east England for another 24 hours from 9am on Friday.
Regions further west including Manchester and most of Wales may be affected on Thursday but should escape the second round of storms, according to the Met Office.
Get in touch with our news team by emailing us at email@example.com.
For more stories like this, check our news page.
Get your need-to-know
latest news, feel-good stories, analysis and more
Thanks for reading the whole article. If you wish to get an daily update about Today could be hottest day of the year with temperatures reaching 30C , click on the bell button to subscribe for the notifications.