Grazax, taken as a pill, provides immunity to the allergens contained in grass pollens and has had an 83 per cent success rate in tests. Allergy researchers believe it will provide relief for hay fever sufferers who find antihistamines and nasal sprays ineffective.

Professor Stephen Durham, of Imperial College London, who is investigating the long-term benefits of the drug, said: “It’s been shown to be associated with a 30 per cent reduction of hay fever symptoms and a 40 per cent reduction in the need for other medications, like nasal sprays.

“We know it’s effective, we know it imparts improvements in the quality of life of patients and we know it reduces the need for treatment.”

There are about 12 million hay fever sufferers in Britain, 95 per cent of whom react to grass pollen, with 13 to 14-year-olds particularly susceptible.

Traditional anti-histamine treatments reduce hayfever symptoms by 10-20 per cent and steroid nasal sprays by 20-30 per cent. These have to be repeated frequently and do not work for all patients. The effects of a spray wear off in about a week whereas a course of the pills — one a day for eight weeks — should keep hay fever at bay for a season.

The drug is similar to the monthly desensitisation injections that provide immunity to hayfever. It works by exposing patients to a 15mg dose of timothy grass extract — one of the worst pollens for sufferers — which kick-starts the body’s immunity response against pollen from temperate grasses.

Tests suggest that unlike injections, which cause serious reactions in 1 in 500 cases, the tablet’s side-effects are limited to localised itching.

Professor Durham, head of allergy and clinical immun- ology at Imperial College, said: “One in four people suffers from hay fever. It can have a severe effect on quality of life; it interferes with sleep, and interferes with work, and children with hay fever can drop a grade at school. I believe about 10 per cent of the hay fever population, potentially a million patients in the UK, could benefit from this treatment.”

The cost of the tablets, which are made by the Swedish company ALK-Abello, has not been decided for Britain, but in Germany they cost about £2.45 each. On this basis, an eight-week course could cost patients about £135, with the potential cost to the NHS £140 million.

The NHS spends about £40 million a year on prescription medicines to treat nasal allergies, including hay fever, and the over-the-counter market is worth another £80 million. Grazax would potentially replace some of these.

Grazax will be available from specialist hay fever clinics, with patients requiring the treatment on the NHS needing to be referred by their doctors.

Further studies are now being undertaken to find out if the pills will provide long-term immunity or if they will have to be taken every year.

Hay fever occurs in varying degrees of severity and can be dangerous for patients with conditions such as asthma. The sneezing, runny noses and watery eyes can last for weeks at a time and affect every facet of a sufferer’s life, awake or asleep. Of the 150 species of native grass in Britain, 12 are responsible for the vast majority of grass pollen.

Grazax has already been approved for use in 27 European countries. The pills will cost £67.50 for 30 days, making the eight-week course £135.

The drug will be initially aimed at the relatively small proportion of hayfever sufferers who either do not respond to conventional treatments or get little relief from antihistamines and nasal sprays.

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