She lives alone and manages them well - but when her sister sounded "delirious" on the phone on Wednesday morning, Maria knew her relative needed an ambulance and it "could have been the worst day for this to happen".

Miss Brennan, 57, has grade 4 cancer in both lungs, is a kidney transplant patient, has severe rheumatoid arthritis and is registered blind.

She lives alone in Newton Abbot, Devon.

Maria, who asked for her surname to be withheld, told Sky News Miss Brennan is "very independent" and "switched on" with managing her health issues.

But when the sisters spoke about 8am on Wednesday, Miss Brennan seemed to be semi-conscious and "drifting off".

"I really panicked," Maria, 63, said.

"Knowing the strikes were on, it really terrified me."

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Miss Brennan managed to tell her sister she had called an ambulance half an hour before, but with paramedics on strike the call handler "didn't know how long they'd be".

She had been sick on herself but couldn't get out of bed to get water. Maria, who lives in London, was worried about her getting dehydrated in the time it took for an ambulance to arrive.

On Monday, Miss Brennan had also been forced to call an ambulance and on that occasion it took seven hours to arrive. With ambulance workers on strike, Maria anticipated the response time on Wednesday could be even longer.

She called 999 from London and was put through to the London Ambulance Service, which promised to communicate with South West Ambulance Service.

Fortunately, Maria's cousin lived nearby and she asked her to go round to check on Miss Brennan.

But when the cousin arrived and entered the house, Miss Brennan "couldn't get out of bed, let alone down stairs", leaving them with no choice but to wait for the ambulance.

Miss Brennan "had started to go blue at the lips" when the ambulance turned up about 11am, three-and-a-half hours after the first 999 call.

The paramedics gave her oxygen and a saline drip and had to stretcher her down the stairs, Maria said, before taking her to Devon and Exeter Hospital.

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When Maria called the hospital she was told they were "completely inundated", but she added: "Everyone I've spoken to has given me time - they've all been angels really."

"Even though they're on strike today they've still done my sister good."

She said the fact they were able to get an ambulance today shows the striking workers were "not leaving people in the complete lurch".

Maria said: "It could have been the worst day for this to happen for my sister but she's still where she needs to be."

She said she worries when NHS staff go on strike "but I think they're doing it for us".

"I think they're genuinely worried about the collapse of the NHS. And they've got no option really," Maria added.

"I'm behind them, even though I was scared about today."