Scottish entrepreneur and philanthropist Sir Tom Hunter has made a £1million donation to dementia charities after being moved by the story of a former music teacher who has the disease.

Paul Harvey, 80, composed a piece of music based on just four notes and captured the mood of the nation with his composition with the video having more than two million hits on social media.

It also moved Sir Tom when he saw a video of the piece being performed.

He surprised Mr Harvey and two dedicated Alzheimer charities live on TV on Monday when he revealed he wanted to make a £1m donation to the organisations.

Speaking on BBC Breakfast, Sir Tom said Mr Harvey lit up the screen.

Sir Tom told the programme 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.

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.

The video clip went viral and the performance was aired on radio for World Alzheimer’s Day on September 21.

The Alzheimers' Society tweeted their reaction to the donation saying: " A huge, huge thank-you to Sir Tom Hunter and to the incredible Paul Harvey. Your support will make an extraordinary difference to families affected by dementia."

While Music for Dementia UK said the donation was more than they could have hoped for.