Conditions will be cooler along the east coast and there is a risk of isolated rain showers in southern and western regions later on Monday.
In Scotland conditions will be slightly cooler but still warm, with Edinburgh likely to enjoy highs of 20C.
“We have got high pressure moving at the moment giving most of the UK a lot of fine weather, this combined with the fact that the high pressure has dominated for the past few days is allowing the temperatures to heat and build,” Marco Petagna, a Met Office forecaster, said.
“It is allowing some record-breaking temperatures to be set today and potentially tomorrow [Monday] as we are looking at a high of 25C or 26C.”
Despite the warm spell, unsettled spring weather will return to the UK later next week.
Tuesday is expected to be mostly dry and warm, according to the Met Office, but the southwest may see some rain showers later in the day.
By Wednesday and Thursday temperatures will be distinctly cooler.
The Met Office said that by the middle of the week there was a risk of hail and thunder in the UK.
Temperatures at their highest on Wednesday are expected to be 14C in London, 18C in Birmingham and 13C in Edinburgh.
Additional reporting by agencies