The LAS received 7,751 emergency calls on Monday – including double the number suffering from breathing problems.
More than 500 patients have been found collapsed after fainting or gasping for breath due to allergic reactions to “very high” pollen levels.
The Met Office has warned that the so-called “pollen bomb” is expected to remain very high in the capital for the rest of the week. Temperatures are expected to reach 30C - leaving London hotter than Ibiza.
The number of 999 calls received by LAS on Monday is the most in a day since the Omicron variant caused a massive influx of people being hospitalised with covid over the 2021/22 festive period.
Ambulance chiefs have suspended all “non-patient facing” activity such as training and boosted the number of ambulances on the road by about a third in a bid to cope with demand.
The service has moved to its highest alert level – known as “REAP 4” – in a bid to ensure the most at risk patients are prioritised for help and waiting times are minimised.
Mayor Sadiq Khan has issued a high pollution alert for Tuesday.
Dr Fenella Wrigley, LAS’s chief medical officer, told the Standard on Tuesday: “Since the end of last week, when this warm spell started, we have got busier and busier.
“Yesterday [Monday] we received 7,751 ‘999’ calls, which is on a par with New Year’s Eve and New Year’s Day of 2021/22, which was one of the peaks of covid in London.
“We have seen an increased number of patients calling for help through the ‘999’ system with symptoms that can be attributed to the warm weather – collapses, dehydration, breathing difficulties.
“Yesterday we saw 529 patients with breathing difficulties that we needed to respond to quickly. That is almost double on a normal Monday.”
LAS said it treated 529 people who had fainted or were suffering breathing difficulties on Monday - double the number a week earlier. This was “due to the higher temperatures and very high pollen count”.
About 200 of the patients with breathing difficulties were classed as “category one” – meaning they had been assessed by LAS call handlers as having “significant breathing difficulties” and required immediate help. The target response time for a “category one” call is eight minutes.
The scale of demand has lengthened the wait for an ambulance for lower category patients. Those in category two, where the target is 18 minutes, faced waits of about 42 minutes last week.
Tree and grass pollen are at high levels. These can cause symptoms such as itchy eyes, a runny nose and a cough due to the allergic reactions they cause.
Dr Wrigley said more ambulances were on the road - while hospitals were being asked to make patient handovers at A&E as quick as possible to enable emergency crews to answer subsequent calls.
“We have moved to our highest resource escalation level and increased our ambulances to over 400 to be able to respond at our quickest,” she said.
Thunderstorms have increased the pollen problem. The movement of warmer and cooler air during and after a storm increases the pollen count in the atmosphere, increasing the likelihood of allergic reactions.
Ms Wrigley said pollen sufferers had included children and young Londoners, including people were out walking or exercising. Homeless people were also at high risk, she said.
Dr Wrigley advised Londoners to remember to carry any inhalers and take antihistamines. Medicines such as Piriton are available over the counter to treat hay fever.
She urged Londoners seeking help to call their GP or NHS 111 first for advice. Any serious cases would then be automatically referred to the LAS call centre.
