Forecasters have predicted weekend temperatures of up to 21C, with Saturday set to be the second hottest Halloween ever recorded.
The hottest ever was recorded last year at Kew Gardens, London and Gravesend in Kent, where temperatures reached 23.6C, according to the Met Office.
This Saturday is expected to replace Dartford, Kent's reading of 20C, measured in 1968 as the second hottest.
Richard Chapman, spokesman for The Weather Network, said that for England and Wales, it should be a largely dry day, "apart from a few spots of rain near western coasts".
He added: "Generally a lot of cloud associated with a weakening cold front in western areas, whilst central, southern and eastern areas should see plenty of sunshine.”
Met Office forecaster Nicola Maxey said that the South-east would experience higher temperatures than the rest of the country.
“London could see 19C or possibly 20C on Saturday if sunshine is pro-longed, with the mid-teens for much of the UK and the Southeast may see higher," she said.
Temperatures are set to rise even in Glasgow, and further north is expected to hit 17C.
“Sunday is expected to be generally fine and the combination of sunny spells and a balmy southerly air stream could allow temperatures to approach an exceptionally warm 21C in the south," Mr Chapman said.
And in a fitting way to end Halloween, forecasters are also predicting a spooky fog forming soon after midnight on Saturday.
The unseasonably warm weather is expected to continue on into Sunday, and a plume of hot air from Portugal is to blame, according to ITV weather forecaster Lucy Verasamy.
