You are the only person I know.. including numerous well informed medical practitioners and organisations such as the NHS etc...who believes that.
Like I said - track down possibly "THE" UK expert and take it up with him. He was obviously talking total kack on whatever R4 science programme it was.
Even one part of the NHS website says that differences in symptoms between cold and flu virus infection do not really exist.
I will say again, you are talking about what is actually infecting a person NOT the symptoms. When anyone says that they have a cold, they DO NOT mean, I am infected with XYZ virus, they mean that they have a blocked/runny nose, are sneezing, have a sore throat and frequently have a cough. The influenza virus can and does do EXACTLY the same to some people - almost certainly me included, thankfully - I have no wish whatsoever to have influenza symptoms ever again.