The incidence of drug-resistant tuberculosis is rising in the UK, researchers warn this morning.

Government scientists studied the latest TB resistance trends by studying data on 28,620 infections in England, Wales and Northern Ireland between 1998 and 2005, and found that in this period the proportion of cases resistant to any first line drug rose from 5.6% to 7.9%. Experts warned that while rates were still relatively low, the enormous cost of treating resistant forms of TB, together with doctors' unfamiliarity with the condition, meant there were serious implications for the NHS.

Dr Michelle Kruijshaar from the Health Protection Agency in London, who led the study, said: "The observed increases highlight the need for early case detection, rapid testing of susceptibility to drugs, and improved treatment completion."

Outside London a significant increase in resistance to one key drug, isoniazid, was linked to immigration. Many of these patients came from sub-Saharan Africa and the Indian subcontinent where they may have developed resistance to the drug, according to the researchers' report in the British Medical Journal.

In London, an increase in resistance to isoniazid could be traced to an ongoing outbreak which began nearly ten years ago, the authors say. To date, it has involved more than 300 cases, including many prison inmates and drug users. The isoniazid problem in London was blamed on poor transmission control.

Multidrug resistant cases showed a small increase from 0.8% to 0.9%, similar to the incidence seen in other western European countries. Professor Peter Davies, lead clinician for the National Multi-Drug Resistant Tuberculosis Service (MDRTB Service), said: "The problem with drug-resistant tuberculosis is that it is still relatively uncommon but increasing. Individual clinicians will have very little experience in managing cases."

"By assisting clinicians in the management of cases of drug resistant TB the national MDRTB service offers our best hope in overcoming the increasing problem of drug resistance until new drugs become available."

Dr Mario Raviglione, director of Stop TB, part of the World Health Organization, said: "The study also proves that no country, no matter how rich and developed, will ever achieve elimination of TB until TB is under control globally. He noted that the cost of treating a patient with MDRTB was 100 times higher than for a normal TB case.

Professor Geoffrey Pasvol of Imperial College London, said:"This is indeed a study of concern, highlighting the increasing occurrence of drug resistant tuberculosis. Resistant tuberculosis is hard to treat for a number of reasons, particularly because of the side effects of second-line drugs for the patient, the prolonged length of treatment necessary, and the high costs."