The man's wife approached the security podium in store to ask for assistance as her husband had taken ill outside.
Iain gave the man first aid while telling his wife to dial 999.
An ambulance crew arrived promptly and said Iain’s diligence had saved the customer’s life, on December 11.
The man was rushed to St. John’s hospital where it was discovered he had a bleed on the brain.
He recovered well in hospital and was able to leave a few days later.
Iain said: “My partner saved my life a few years ago when I had a heart attack and her quick actions meant I got the care I needed.
"I feel grateful that I was able to help this man. When I saw him, I immediately knew that something was seriously wrong, and my first aid instincts took over.
"I was happy to help and glad that I made a difference.”
Jackie Martin, Admin Manager at Asda Livingston, said :“We are so proud of Iain, he is a true hero. Iain jumped into automatic mode and his calm exterior and clear head helped to save the customer’s life.
"He is very diligent and a real team player who is always looking out for his colleagues and customers. I am so glad he was on duty and able to assist.”