Meteorologists have warned that flash floods could hit parts of the UK after the hottest day of the year so far was recorded on Monday.

The Environment Agency and the Met Office made their warning after temperatures rose to as much as 32.8C (91F) in Gravesend in Kent.

The agencies said parts of southern, central and eastern England could see heavy rain develop on Tuesday that could lead to localised flooding. But this was likely to come from surface water rather than rivers.

The change in weather came as two police dogs died in a locked car and express train services were slowed by overheating wires, as temperatures in the UK came close to matching the Caribbean for three days.

Temperatures reaching this year's record of 31C in London claimed the lives of a German Shepherd puppy and a working Belgian Malinois which collapsed at the Metropolitan police dog training unit. Police and animal welfare groups were investigating and a national warning was issued to pet owners after two other dogs were rescued by officers who broke into cars parked in Bath.

A spokeswoman from the Dogs Trust, the UK's largest dog welfare charity, said: "We would like to remind dog owners and police dog handlers that leaving your dog in a car can prove rapidly fatal, particularly during a heatwave. It can take just 20 minutes for a dog to die and the heat can reach over 40 degrees in some vehicles."

Temperatures rose particularly rapidly in the wake of a "Spanish plume" of warm air driven north from Morocco and Spain and curling round most of the UK, holding colder weather from the north at bay.

The pattern is breaking up as airstreams alter and the mini-heatwave has started to end with thunderstorms in southern England, where temperatures have been highest, while gentler rain moves south across the border from Scotland.

The Met Office warned that downpours in parts of southern and eastern England and the midlands could be heavy enough to cause flash floods. A spokeswoman said that rivers were not expected to break their banks but predicted highly localised rainfall of between 25mm and 50mm could overwhelm drains and cause surface water flooding.

A spokesman for the Environment Agency said: "Our staff are on 24-hour alert, and teams are monitoring river levels as the band of rain moves across the country. The public are encouraged to tune in to local media for weather forecasts for their area and to keep an eye out for signs of surface water flooding."

A hot weather warning from the Met Office remains in force for southern England, the home counties and the midlands, after temperatures rose to within 1C of the day's 32C recorded in Kingston, Jamaica. The spell just failed to beat last year's record of 31.7C set at Gravesend in the first week of July.

Absenteeism was widespread after weekend forecasts that Monday would be the hottest day of the year so far, and the working day was also disrupted by the wrong kind of heat on electric rail services. Trains between East Anglia and London were slowed from their usual 90mph maximum to 60mph because of concern that power might short or be lost through other glitches with sun-drenched overhead cabling.

A spokeswoman for Network Rail said: "We're already doing weekend work on overhead wires on this route and they can overheat in very hot weather. Initial speed cuts of 80mph were initially introduced and then lowered further in the hottest part of the day."

Elsewhere, the warmth engulfed almost everyone fortunate enough to be outdoors, from Andy Murray who disposed easily of his French rival for a place in Wimbledon's last 16, to litter-pickers at Glastonbury.

Schoolchildren marooned by the tide on an outing to St Mary's Island off Tyneside picnicked in the sunshine. Nearby Newcastle upon Tyne celebrated the discovery of natural hot water under the city centre by a trial borehole, while lunchbreakers sat under palm trees newly-installed on the riverside, in the year's best temperatures of 22C.

MeteoGroup forecasters said that the last outposts ofhot and humid weather would clear , with fresher conditions for the rest of the week and scattered showers.

London is expected to see a particularly rapid drop in temperature but the weather will still be pleasant at a predicted 24C. Umbrellas and the Centre Court roof at Wimbledon are likely to be in action, however, with almost certain thunderstorms and heavy rain at times.

Paul Mott, of MeteoGroup, said: "By Wednesday the heatwave will definitely be over. If anything it will be a bit colder than average, 20C in London and down to 15C elsewhere."

In Wales, warmed by the Gulf stream, things were better and contented visitors included Prince Charles, who disappeared briefly behind a large strawberry ice cream during a tour of Aberdyfi, on the coast of Gwynedd.

The Met Office said cooler weather would persist until next weekend, but most of the UK would be fine and largely dry once the post-plume thunderstorms had passed on.