The number of people admitted to hospital with life-threatening allergic reactions has more than doubled in a decade, according to the latest figures.

Allergy specialists said as many as a million people a year may suffer an anaphylactic shock – sudden swelling, breathlessness and low blood pressure – and the surge in admissions was only the tip of a larger problem.

Britain is in the grip of an epidemic of allergic disease and anaphylactic shock is its severest manifestation. Hospital admissions for anaphylactic shock rose from 1,558 in 1997-98 to 3,385 in 2007-08, official figures show.

The number of deaths from anaphylactic shock trebled from eight in 1998 to 24 in 2007. Specialists said this understated the true number because by the time patients got to A&E they might have trouble breathing and be wrongly classified as having an asthma attack.

The numbers of people affected by allergies have trebled in the past 20 years and it is estimated that a third of the population will develop an allergy at some point in their lives.

Pamela Ewan, consultant allergist at Addenbrooke's Hospital, Cambridge, said: "The hospital admission figures rose seven-fold between 1990 and 2000 and these figures show they have risen again. They are the tip of the iceberg. Very few patients get admitted – the vast majority are treated in A&E and discharged."

Dr Ewan said the rise in anaphylactic shock was unexplained but reflected the general rise in allergies.