A Beckenham family's plans of enjoying a BBQ on the hottest day of the year were scuppered by an unexpected party guest.

John and Debbie Smith were spending time with grandkids when their daughter suddenly went into labour ten weeks early in their hallway.

Temperatures soared 35 degrees on June 29 and the couple had only returned home to Beckenham after visiting their other daughter in Eastbourne.

They considered staying another night but Debbie, who is 59 today, decided to come back to see how Scarlett was doing.

Grandkids were playing the paddling pool when Scarlett, who lives in West Wickham, arrived to tell her mum she didn’t feel well.

After lying down upstairs, Scarlett, 30, came down later to say it was time to go to the hospital, before leaving the toilet minutes later claiming she could see the baby's head.

"The next minute it was pandemonium," Debbie, who is 59 today, told News Shopper.

John, 60, dialled the ambulance and an "amazing" controller on the phone gave instructions over loudspeaker.

The grandad rubbed his daughter’s back and tried with all his will not to drop the phone or lose the connection.

Debbie’s mum, 79, was trying to distract the young kids in the garden as Scarlett was in the hallway giving birth.

"It was just quite unbelievable," Debbie, who successfully delivered her granddaughter Dusty, said.

"The baby was so very tiny and wasn’t crying. I recently watched the Emma Willis midwife programme and you pick up a few bits.

"I had to move the cord from the baby’s neck, and it went through her legs, so for six minutes until the paramedics arrived, we didn’t even know if it was a boy or a girl."

Scarlett's mother in law Mary quickly arrived on the scene to add to the collective help. 

Debbie praised her family for what was a scary few minutes when you couldn't help but fear the worst.

One of the most beautiful moments was when little Dusty finally let out a cry.

"You watch all these soap operas and you see all these things going on," Debbie said. "I always say to my husband that this never happens in real life, but I’m eating my words now."

The family was blown away with how the emergency services handled the situation.

Paramedics arrived to the cut the umbilical cord and Debbie said the "wonderful person" on the phone and the first responders were phenomenal.

"I didn’t even get to say thank you to the man," Debbie said. "I’ve been Googling it and apparently they get a pin when they deliver a baby over the phone.

"I hope he gets one because he deserves it."

Scarlett and Dusty are now doing well and the baby remains in King’s College Hospital.

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Her husband, Daniel, who is an actor, was preparing to go on stage when the unexpected birth happened.

Dusty is their first ever child and Debbie said: "They are unbelievable with the baby and they sit and have cuddles with Dusty.

"They are going to be the most wonderful parents and it is beautiful seeing the three of them.

"I think they are now saying it will be their one child now though," Debbie laughed.

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She also joked that husband John said they can never move from their Beckenham home after what happened.

Debbie often walks down the stairs and smiles after remembering the magical moment.

Scarlett and her husband are staying in the Ronald McDonald House until they can finally welcome Dusty back home again.