Hampstead Heath is on fire alert after soaring temperatures which resulted in Parliament Hill Lido shutting its doors early for the first time in nearly a decade.

The City of London Corporation, which owns the beauty spot, this week issued blaze warnings amid growing concern over the tinder-dry conditions.

The Corporation reminded visitors of a blanket ban on barbecues and urged smokers to take care when disposing of cigarette butts.

Thermometers recorded temperatures as high as 32C in the capital at the weekend, drying out the grass in the park.

The London Fire Brigade also issued a warning yesterday about grass fires, saying it was dealing with 21 incidents a day across London, compared with five per day last July.

A spokesman for the City said: “There is a serious fire risk during the current heat wave. We are operating a zero-tolerance policy to barbecues – which are a major fire risk on the Heath’s peaty ground – and we would encourage the public to make sure that any cigarettes are fully stubbed out to minimise the danger.

“There is such a risk in areas with dry grass and wooded areas, which in some places are bone dry.”

Heath Constabularly officers have been equipped with water bowsers so they can react quickly to any flames, as staff brace themselves for another record-breaking weekend.

About 80,000 people took to the Heath on Saturday and Sunday while the Parliament Hill Lido and bathing ponds had 18,000 swimmers over the two days.

Queues to the lido stretched for almost a quarter of a mile to Gospel Oak station, with visitors waiting well over an hour for admission. At 3.30pm on Saturday it was shut for the first time in eight years due to the crowding inside.

Lido team leader Glyn Roberts said: “I have worked in the lido for 20 years and I have never seen anything like it.”

Lifeguards made more than 30 rescues from the lido as well as 12 from the Mixed Pond on Saturday alone.

About 12,000 bathers also enjoyed the Heath’s three swimming ponds. Swimming supervisor Paul Jeal praised the Heath’s lifeguards for “first-class” efforts on 12-hour shifts in the searing heat.