A chance encounter proved to be life-saving for a St Albans woman who unexpectedly collapsed.

In late June, a group of Maple Primary School mums - Christina Brown, Susie Hawkes, Deni Boncheva and Martha Lund - had gathered at about 7.30am for their first run as a group.

Jogging towards the bridge off York Road, they stumbled across a woman who had collapsed.

Christina said: "As we were running we saw a lady on the ground, sprawled on the floor, face to the ground.

"We initially went 'oh how awful, she's had too much to drink'. But then we realised quite quickly she wasn't breathing properly and she was very grey."

Anna Thompson had been on her way to meet her husband, who was waiting to see the Flying Scotsman pass under the bridge, when she suffered a sudden cardiac arrest.

The group acted quickly, with passer-by David Hope calling 999 and Christina starting CPR.

Christina, who is 41 with two children, said: "The operator told me the pace to do it and I basically did it as hard as I could because I knew instinctively that I needed to do it hard. I needed it to keep her alive."

The immediate moments following a cardiac arrest are crucial - according to a Consensus Paper on Out-of-Hospital Cardiac Arrest in England published by the British Heart Foundation and Resuscitation Council UK, every minute without CPR and defibrillation reduces a person's chances of survival by seven to 10 per cent.

An ambulance quickly arrived to take Anna to hospital, where she was placed into a coma.

Christina added: "It was all very emotional. We went and did the run around Clarence Park afterwards because we didn't know what to do with ourselves.

"Whenever we go for a run now I hope that if someone collapses that it is us who finds them, because we know what to do."

Anna, who is a primary school teacher with a teenage son and step-daughter, spent three weeks in hospital and is now on the road to recovery.

She thanked paramedics on the scene and staff at Watford General Hospital and Hammersmith Hospital for their care and treatment.

The 39-year-old has no memory of the day she collapsed: "When I came around in hospital it didn't sink in straight away.

"I thought something else had happened and everyone was making a fuss about nothing. But no, I now realise if Christina had not been there, I would have died.

"I just love her and I am so grateful. I consider her to be my guardian angel because she saved my life. I really love life, I always thought I would live to 100 and still want to live to 100. She has given me that chance.

"She has given me the gift of carrying on with my life."

It is unclear what caused Anna's cardiac arrest and she is currently undergoing tests. However, she has already had an internal defibrillator fitted.

This should activate to automatically save Anna's life if it detects another cardiac arrest.

Anna said: "We know it is almost certainly nothing to do with lifestyle, it is more likely a genetic condition, but there are none in my family.

"If the tests come back as not genetic then we will put it down to a mystery.

"My friends are shocked. I don't smoke and hardly drink and I am very healthy so it is been scary for people in a way - if it could happen to me it could happen to anyone."

Since the incident, Anna and Christina met up at The Ivy St Albans.

Anna said: "I feel like having met her I can see she is capable of acting quickly and decisively. I was really lucky that she was there, knew what needed to be done, and said 'I am going to do it'.

"It was so lovely to meet her, I had heard all about her because my family had talked about her so much.

"I just wanted to hug and cry and it was just really nice to get to know her as a person and find out about her."

Cardiac Risk in the Young (CRY) is a charity which provide young people with screenings to detect undiagnosed heart conditions.

These have no symptoms in 80 per cent of cases. Find out more at www.c-r-y.org.uk

Visit www.bhf.org.uk for more information on CPR and heart conditions.