One day a colleague advised him about drinking on duty, prompting John to seek medical help; he didn't drink.
Tests revealed he had CIDP, a rare form of Guillain Barre Syndrome (GBS) - a neurological condition that affects feet and hands and can rapidly cause paralysis.
Although there is no cure, treatments have proved effective and the majority of people make a full recovery. The likes of Tony Benn and Morton Wieghorst are among the better-known cases.
But John didn’t recover and when doctors investigated, they diagnosed Motor Neurone Disease (MND), telling his wife Catherine that he wouldn’t see the end of the year.
John was virtually unique in being diagnosed with both GBS and MND and eventually he succumbed in 1998.
Despite the subject matter and underlying presence of a life slipping away, the display acts as testament to John’s love of life and resolution that no matter how bleak life is, there’s always hope.
This is reflected in the name of the Dochas Fund, the charity he founded with his wife Catherine. Dochas is Gaelic for hope and also the motto of his adopted hometown, Lochgilphead in Argyll.
Using his art to help others was the perfect way to give his work a real purpose. So, cards and prints of his work were produced and their sales continue to support others whose lives are affected by either of the conditions he suffered from.
For more information about the charity John and his wife set up, visit the Dochas Fund website.