Flowers have been laid in tribute to a teenager who died after allegedly taking laughing gas at a party in Thamesmead.

UPDATE: Met Police apologise to Sidcup teen Alistair Calvert's family after suggesting Thamesmead death was linked to laughing gas

The 18-year-old, named locally as Ally Calvert, collapsed in Wolvercote Road after suffering a cardiac arrest at around 11.15pm on Saturday.

Paramedics rushed him to a south London hospital where he died two hours later at around 1am.

He is thought to have been drinking alcohol and ingesting legal high nitrous oxide, also known as laughing gas, police say.

Today (July 25), devastated friends left bouquets of flowers with loving messages at the spot where the teenager was found collapsed near the entrance of Clewer House, a block of flats.

Two friends, aged 17, who would not be named, said they had not seen him take any laughing gas at the party.

One of them said in tears: "He was the nicest person you could ever meet. He was always happy and smiling.

"We were at the party with him just five minutes before. I can't believe this has happened.

"He only had one beer at the party. I didn't seem him have any laughing gas at the party and I've never seen him doing it before.

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Floral tributes laid at the spot where the teenager collapsed

"We were at school together although he was in the year above. He had left to go to college. He wanted to be an electrician.

"He had just got back from a boys' holiday. He's got a brother and a sister."

Jenny Oliver, former teacher and exams officer at Cleeve Park School, Sidcup where Ally attended, told News Shopper: “He was a wonderful young man, popular without being loud, a friend to all.

“This really is so out of character for him, he was a well brought up lovely young man with no history of dabbling drugs or substances.”

Mother of three Christine Villiers, 31, who has lived in the block for four years said that she and her partner were coming home when they saw the police and paramedics outside the entrance.

She said: "They were giving this young lad compressions on the floor trying to keep him alive. He looked in a really bad way.

"It was really upsetting. We hoped he would live but we heard today he had died.

"I understand that he had been at a party elsewhere on the estate and collapsed here as he made his way home. It's awful.

"You see empty silver canisters everywhere so you know loads of people are using it. I feel so sorry for his poor parents."

A 22-year-old woman in the block who did not want to be named said: "The poor boy was laying unconscious. He was naked and they were trying to resuscitate him.

"He was in a really bad way, I remember he was really pale.

"There was quite a few people watching.

"A police woman was talking to two of his friends. I heard them say they had been at a party and were on their way home.

"It is a real tragedy. You see the empty canisters everywhere on the estate. People take it but obviously don't realise how dangerous they can be."

A friend named Charlie had left a heartfelt note with flowers, which read: “Rest in peace. A young life taken too early. You’ll be missed.”

Two others, Ollie and Josh, had written: “Ally, one of the nicest boys I know. Had so many laughs with you. Never going to forget about you Ally. RIP.”

Another message said: “I can’t believe what’s happened. RIP Ally, you’ll never be forgotten. Lots of love forever and always. Sleep tight.”

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Moving tribute: A heartfelt message left at the spot where the teenager was found collapsed

Seventeen people in the UK died between 2006 and 2012 after taking the legal high.

On Friday, Bexley police posted a warning about the dangers of nitrous oxide on its new Facebook page.

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It is not illegal to be in possession of nitrous oxide but it is prohibited from being sold in England and Wales to under-18s if there is a risk they will inhale it.

The gas gets its nickname from its ability to make people feel relaxed, euphoric and giggly.

But abusing the substance can lead to oxygen deprivation causing loss of blood pressure, fainting and heart attacks.

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Wolvercote Road, Thamesmead (Photo: Google)

Next of kin have been informed and a post-mortem will be scheduled in due course.

A Met Police spokesman said: “At this stage the death is being treated as unexplained pending the findings of the post-mortem.”

Enquiries continue and Bexley police investigate.