The family of Sidcup teenager Ally Calvert have denied his death was linked to laughing gas – as police confirmed a post-mortem exam was ‘inconclusive’.

The 18-year-old collapsed in Wolvercote Road, Thamesmead, at around 11.15pm on Saturday after attending a party with friends.

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

On Sunday, Met Police said they believed Ally had “ingested nitrous oxide and alcohol” shortly before he died.

Nitrous oxide, better known as laughing gas, comes in small, silver canisters and is inhaled through balloons; generating feelings of euphoria and even hallucinations in the user.

Today, (July 29) a Met Police spokesman said: “A post-mortem examination has proved inconclusive.

“The force awaits further toxicology results.”

But Ally’s friends and family, describing him as “a beautiful, charming, hilariously funny 18-year-old baby”, say he died due to an undetected heart condition.

In a post shared on social media, a relative wrote: “As a family, we would like to express how overwhelmed we have been with the support for the recent loss of Ally.

“We can now confirm, that the use of balloons/nitrous oxide did NOT cause the death of our baby, as we originally knew anyway.

“Ally had an underlying heart condition which lead to his passing.

“Unfortunately regardless of where he was, or who he was with at the time, his passing was inevitable and this is the facts.”

Friends and family have launched a memorial fundraising campaign, ‘Ally’s Big Heart’, to support heart condition research charities.

The campaign, which has been trending on Twitter under the hashtag, #AllysBigHeart, has been endorsed by former Manchester United player and England captain Rio Ferdinand.

The 36-year-old said on Twitter: “@Allysbigheart. Far too young. Raise awareness.”

Queens Park Rangers FC also lent its support, tweeting: “#AllysBigHeart”.

Speaking to BBC London radio last night, Met Police Commissioner Bernand Hogan-Howe voiced his concerns at the popularity of laughing gas across the capital.

He said: “When I go out on patrol at the Notting Hill Carnival the street is littered with canisters.

“It obviously affects people’s behaviour and they get some kind of high from it.

"Just to be walking that distance, there is a huge amount of litter of this stuff about.

“There is a law going through this year in Parliament about psychoactive substances and I suspect it is one being considered and is going to be banned.

“Now, how dangerous it is compared to other things I am not in a position to say.

“But the amount of use of it makes you wonder whether combined with other things such as alcohol and other drugs it could be an awful cocktail.

“Certainly in this case it has led to a terrible outcome.”