London - Sunbathing, pollution and an increase in the use of antibiotics could be contributing to an alarming rise in blood cancers in Britain, medical experts say. A new study of leukaemia, lymphoma and other blood diseases, the largest of its kind in Britain, showed a 40 per cent increase in non-Hodgkin's lymphoma (NHL) over the past 10 years in the 30-79 age group. The disease could be the sixth most common form of cancer by 2000.