Hot air from the south will push the weather above average for August - possibly topping the record for the year so far.
Met Office forecaster Alex Burkill said: “Temperatures are likely to climb. At the moment they are a little bit below average for the time of year because of the north-western flows.
He said that a “good chunk” of the country, including Scotland, would enjoy the hot conditions, but that it was a “bit early” to call it a heatwave.
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Bookmakers Coral is odds-on at 1/4 that temperatures will reach 30C or higher before the end of this week, and are offering 2/1 odds that the record high temperature of 38.5C will be broken in the UK this summer.
John Hill, a spokesman for Coral, said: “If the forecasts are correct, we have a two-week heatwave to look forward to this month which has promoted a gamble on this August being the hottest ever and for the record high temperature to be broken in the UK this summer.”