Instances of drug resistant tuberculosis are rising in Britain, experts have warned.
Researchers studied the latest TB resistance trends by studying data on 28,620 infections in England, Wales and Northern Ireland between 1998 and 2005.
During this time, the proportion of cases resistant to any first line drug rose from 5.6% to 7.9%.
Outside London a significant increase in resistance to one drug, isoniazid, was linked to immigration.
Many of these patients came from sub-Saharan Africa and the Indian subcontinent where they may have developed immunity to the drug, said the study authors writing in the British Medical Journal.
In London, an increase in isoniazid resistance could be traced to an ongoing outbreak which began in 1999.
To date it had 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%, a similar incidence rate to that in other western European countries.
More than 8,000 TB infections were reported in England, Wales and Northern Ireland in 2006.
The researchers, led by Dr Michelle Kruijshaar from the Health Protection Agency in London, concluded: "The observed increases highlight the need for early case detection, rapid testing of susceptibility to drugs, and improved treatment completion."