Professor Ted Tuddenham, of Imperial College, London, said that although many people now recognised a link between deep vein thrombosis and travelling on long-haul flights following several newspaper stories, few people were aware that sitting still for long periods of time at home or work presented the same risk.
His warning came as a science teacher described how spending a weekend working at the dining-room table, as she prepared for a forthcoming Office for Standards in Education inspection, landed her in hospital.
Professor Tuddenham said: "It is vitally important that, however pressing your work is, you remember to walk around regularly to keep blood flow moving, especially in the legs."
Science teacher Hilary Ellison was rushed to hospital suffering from a deep vein thrombosis after spending Saturday evening and al day Sunday battling with a "sky-high" pile of paperwork.
She sat virtually motionless for hours on end, relying on her husband and three children to ply her with food and drink.
And she is convinced it was this failure to get up and stretch her legs that caused the clot in her left leg which landed her in hospital for several days.
Hilary, who teachers at a secondary in Hampshire, said: "The doctors kept quizzing me about recent long journeys, smoking and if I was taking hormone replacement therapy - factors believed to be linked to DVT.
"But none of these things applied to me and I was convinced from the start that it was because I had been sitting down without moving my legs for the same amount of time as if I had flown halfway around the world.
"Fortunately, because I was treated quickly, the condition didn't develop into a pulmonary embolism which can kill you. The downside was that I was out of hospital and back to work just in time for the inspection."
Tomlinson promises less stressful inspections, 15