Scotland's public sector complaints watchdog, the Scottish Public Services Ombudsman (SPSO), told the practice in NHS Greater Glasgow and Clyde to issue a written apology after it failed to diagnose Crohn's Disease, an inflammatory bowel disorder.

The failure came despite repeated the man visiting various GPs complaining of stomach problems between April 2005 and November 2009, when he left the practice. He was diagnosed with dyspepsia – indigestion –and irritable bowel syndrome.

He was told he had Crohn's Disease after he moved to another practice where his symptoms were "rapidly investigated". However, by then – November 2010 – he had to have parts of his small and large bowel removed and a stoma bag fitted.

Doctors normally only remove parts of the bowel in extreme cases of Crohn's Disease as a last resort, when other therapies have been exhausted.

Jim Martin, the ombudsman, said the practice should have been "more proactive" in reconsidering its earlier diagnosis of dyspepsia and irritable bowel syndrome when Mr C complained of ongoing bowel symptoms in 2009.

An expert medical adviser said the symptoms pointed to Crohn's Disease as early as 2005.

In a separate case in NHS Borders, the SPSO criticised another GP surgery over an "avoidable delay" in diagnosing a 57-year-old man with diverticular disease, a condition affecting the colon which causes abdominal pain and diarrhoea.

The patient, known as Mr A, visited his GP several times between December 2010 and February 2011 due to bowel problems and, from February 11, 2011, onwards, complaining of pain in his groin.

He was diagnosed with diverticular after undergoing a CT scan which flagged up "extremely serious" findings. He was prepared for emergency surgery within hours and had part of his bowel removed.

The SPSO has demanded a written apology.