A man in his 50s was killed when a tree fell on the Peugeot 307 car he was driving in Lower High Street, Watford, at around 6.50am, Hertfordshire Police said.
Officers closed the road to deal with the incident but the man, from Harrow in north west London, was pronounced dead at the scene.
Meanwhile, a 17-year-old girl was killed in Hever, Kent, when a tree blew on to the caravan where she was sleeping at 7.18am.
Up to 220,000 homes suffered power cuts as St Jude’s storm with winds of almost 100mph pushed across the South West, South, South East, the Midlands and the East of England, UK Power Networks said.
Falling trees and other debris covering railway tracks caused travel misery for thousands of commuters, with trains and London Underground services suspended.
The port of Dover in Kent had to shut, more than 130 flights at Heathrow Airport were cancelled and many roads were impassable due to fallen trees.
The strongest gust of wind was recorded at 99mph on the Isle of Wight. The strongest gales were expected to have cleared the mainland by mid-morning with scattered showers and blustery winds remaining.
The Environment Agency said there were 12 flood warnings in place across the South West, the Midlands and the East of England. There were also 131 flood alerts telling people to be prepared for flooding.
A falling tree devastated three houses when it fell on a gas main and led to an explosion in Hounslow, west London.
An elderly woman was taken to hospital following the blast and three people were rescued by London Fire Brigade.
Twelve people were evacuated from surrounding properties as a precaution and fire crews also rescued a dog.
Rail companies said disruptions were likely to last well into the day, with some, including Stansted Express and Greater Anglia, saying they would be unable to run services until at least 12 noon.
Although the Kent port of Dover was reopened, P&O Ferries warned of delays of up to two hours on some sailings.
A double-decker bus “rolled over” in Suffolk, injuring the driver and several passengers.
Witnesses told police the vehicle blew over at 8am, rolling onto its side and coming to a stop in a field in Hadleigh.
The driver, a man in his 40s, was initially trapped and was treated at the scene by paramedics.
A police spokesman said: “He was suffering from neck pain, had taken a bash to his head and was in and out of consciousness.
“There were several other people on board, with a couple of walking wounded. We believe the driver has been taken to hospital. The road is completely blocked.”
In central London, Whitehall was closed both ways between Parliament Square and Horse Guards Avenue after a crane collapsed on to the roof of the Cabinet Office.
During a visit to the Mini plant in Oxford, Prime Minister David Cameron said: “Any injury or loss of life is hugely regrettable.
“We have to make sure the emergency services can act as fast as they can to help people.”