Today will be the hottest April 19 in decades as London is set to swelter to the high 20s.

Temperatures are likely to hit 28C in the capital today, making it the hottest April day in 70 years.

The hot weather far surpasses the average maximum temperature for April, which is 11.4C (53F).

The summery spell comes as a result of warm air from the Azores, off the coast of Portugal, being dragged up towards the UK by the combined efforts of an area of low pressure over the Atlantic and high pressure over western Europe.

A high of 28C would beat the 2001 April high of 27.8C (82F), the Met Office said.

The warmest April day on record was 29.4C (85F) in 1949.

Meteorologist Alex Burkill said: "There's a fairly good chance of 28C, there's about a 60 per cent chance."

A high of 25.3C (78F) was recorded in St James' Park in London on Wednesday (April 18), making it the hottest day of the year so far.

Competitors in the London Marathon can expect hot and humid conditions with a forecast of between 21C (70F) and 23C (73F), Mr Burkill said.

Some hayfever sufferers could be affected by high pollen counts, he added.

Mr Burkill said: "For anyone who suffers from tree pollen they will probably be feeling the effects, but that's only about 20 per cent of hayfever sufferers. Grass pollen season comes later in summer."