SCOTS singer-songwriter Charlotte Gordon Cumming has spoken of the overpowering moment when a friend offered to donate her kidney after undergoing secret blood tests.

Ms Gordon Cumming suffered kidney failure in 2008 after consuming poisonous mushrooms handpicked in the grounds of her brother's estate at Altyre House in Forres, Moray.

The musician, her husband – Horse Whisperer author Nicholas Evans – brother Sir Alastair Gordon Cumming and his wife, Lady Louisa, were rushed to hospital within hours of the family meal, in which they dined on deadly webcap mushrooms after Evans had mistaken them for harmless wild ceps.

After gruelling dialysis three times a week for the past four years, Ms Gordon Cumming says she feels an amazing sense of freedom as she recovers at home in Devon following a successful transplant at Hammersmith Hospital in London last week.

The operation, with a kidney donated by the mother of her 10-year-old son's best friend, came after a string of heartbreaks as other friends and relatives were unable to provide a match.

Ms Gordon Cumming said: "Serena was absolutely amazing. Our sons are best friends and we met on the football pitch. Her husband was the coach of the football team and she is a nurse.

"She could see me struggling with the dialysis. Without me knowing, she went off and did the tests.

"One day we took the boys to play cricket. I said something to her like: 'I just feel so dreadful that I might not even see my son when he's 17.'

"I think something just hit her and she turned around to me and said: 'I've had all these tests done, I'm the same blood group, and I really want to give you a kidney.' It was very, very moving.

"We went for tests and the matching was so good that it was as if she was my sibling."

Ms Gordon Cumming, 54, had never joined the NHS organ waiting list, preferring to hold out for a kidney donated from a live patient.

She and her husband have become vocal advocates for altruistic organ donation, which involves donating to a stranger.

Evans has become patron of the charity Give a Kidney – One's Enough and Ms Gordon Cumming filmed a documentary about her experience on dialysis for the BBC. She is now filming a follow-up about her transplant.

She said: "Very few people know about dialysis and the horror of being kept alive on these machines. These wonderful people who step forward to donate a kidney altruistically are really very special."

Evans has made a full recovery after undergoing a transplant last summer with a kidney donated by his daughter from his first marriage, while Ms Gordon Cumming's sister-in-law, Lady Louisa, who consumed a much smaller amount, was able to come off dialysis after three months as her kidney function improved.

Sir Alastair underwent a transplant at Edinburgh Royal Infirmary two months ago after receiving a kidney from a patient who had died in intensive care. However, Ms Gordon Cumming said she was very upset after the offer by a friend of hers in Devon to donate one of his kidneys to Sir Alastair fell through.

She said: "Edinburgh really didn't want to do this operation with my friend Chris. They had never done this type of altruistic donorship before and they called them a 'new category'.

"Then, strangely, two days later he was rung up in the middle of the night and told there was a kidney. He and Louisa just looked at each other and said 'we have to go for this'.

"His recovery has been much slower than Nicholas and I. I have to say I'm very upset by it because Chris was such a great match, and there's just no comparison between a live kidney and one donated from a dead person."

But four years on from the lunch that nearly killed her, Ms Gordon Cumming said she feels no bitterness over the episode.

She said: "I think it was very hard for Nick but there's no point blaming anyone. It could have been me, it could have been any one of us who made the mistake. I've never felt any acrimony or blame at all."