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The story of a former music teacher with dementia who composed a piece based on just four notes has inspired a £1m charity donation from Scotland's first ever billionaire.

Sir Tom Hunter told ´óÏó´«Ã½ Breakfast when he saw a video of Paul Harvey, 80, performing the piece, he immediately wanted to stump up the money.

Mr Harvey's son Nick had posted the clip online to show how musical ability can survive memory loss.

He "lit up the screen", said Sir Tom.

The donation will be split between the Alzheimer's Society and Music for Dementia.

Mr Harvey, a composer from Buxted, in Sussex, was diagnosed with dementia late last year but has continued to be able to play piano pieces from memory - as well as create new ones.

His son said it had been an "old party trick" of his father's to request four random notes and then improvise a song.

In the video Nick picked F natural, A, D and B natural for his father to play.

went viral and the performance was then aired on Radio 4's Broadcasting House for World Alzheimer's Day on 21 September.

After listeners asked the ´óÏó´«Ã½ to have the performance orchestrated, Mr Harvey recorded it with the ´óÏó´«Ã½ Philharmonic orchestra and it was released as a single on Sunday.

All proceeds will be split between the Alzheimer's Society and Music for Dementia.

Nick said when he told his dad he had reached the number one spot in just days he "laughed and thought I was joking".

He said: "Dad is so happy his music is resonating with people.

"He is being defined by his music, not his dementia and that is wonderful to see."

Sir Tom told ´óÏó´«Ã½ Breakfast he and his wife Marion had been so moved by watching Mr Harvey's "wonderful piece" at a time when people are "searching for good news" they decided to donate £1m from The Hunter Foundation to the two charities.

The entrepreneur and philanthropist told Mr Harvey: "You lit up the screen with, first of all the relationship between the father and the son, and then the relationship with music."

"We really believe music is a key," he said, adding that he had lost both his parents to Alzheimer's.

"We really believe you're on to something and we really want to help," he said.

Mr Harvey said: "That is fantastic, it really is. I didn't think I could be moved much more now - but I can.

"For all this to happen and I'm in my 80s - I think that's pretty good."

"Just think what you'll achieve in your 90s," added Nick.