- 22 updates
Delays of around 20 minutes is expected on the Southern train service to Brighton from London Bridge, as Network Rail blamed "signalling failures".
A spokesman for Network Rail said:
The Met Office has issued a yellow alert for rain, ensuring the public to "be alert" of potential torrential downpours today.
A Met Office forecaster said: "Isolated thunderstorms with very heavy rain, hail and gusty winds are possible later this afternoon and early evening.
"The public should be aware of the risk of very localised surface water flooding, particularly if the thunderstorms affect urban areas".
"These could produce 30 mm of rain in less than an hour, large hail and also squally winds".
The Met Office has extended the heat health warning over London and the south east, with the warning raised to an amber level 3 warning, as temperatures are expected to soar today.
A level 3 amber warning means that social and healthcare services are required to take action for high-risk groups including the elderly and babies and young children.
Britain could turn tropical with high humidity and the hottest day of the year so far, before "violent" thunderstorms bring a dramatic end to the heatwave, according to forecasters.
The mercury is expected to reach 33C (91.4F), with London being one of the likely contenders for the hot spots of the day. The hottest day of the year so far had been last Wednesday at Hampton waterworks, south west London, with highs of 32.2C (90F).