Children living near nuclear facilities are more likely to develop leukaemia, scientists said yesterday.

Incidences of the cancer were up to 21% higher for youngsters aged up to nine, according to a major review of previously published studies in Scotland, England, Europe, Japan and America.

Death rates for the disease rose even more, by up to 24% depending on how close the children stayed to facilities.

Scientists, however, said they did not know why.

Previous studies have always been hampered by the tiny size of samples. Nuclear facilities tend to be in rural areas with small populations and childhood leukaemia is rare, meaning even a very small number of incidences of the disease could skew figures.

The new work, published in the European Journal of Cancer Care, has analysed the results of 17 previous reports, three of them Scottish, to get a more robust scale of study.

Peter Baker of the Medical University of South Carolina, the new paper's lead author, said he did not know why leukaemia rates were higher near nuclear facilities.

He said: "Although our analysis found consistently elevated rates of leukaemia near nuclear facilities, it is important to note that there are still many questions to be answered, not least about why these rates increase. It is clear that further research is needed into this important subject."

Orkney and the Western Isles both have some of the highest rates of leukaemia in the UK and campaigners have linked this to Dounreay, the decommissioned 1950s reactor in Caithness. Radioactive particles have been found on beaches near the site. However, the populations of the islands are too small to provide what most scientists would regard as conclusive evidence of this.

Scotland has some of the highest concentrations of nuclear facilities, both civilian and military, in Europe. Most, like Dounreay, are in rural areas, including the Clyde Submarine Base, the former Chapelcross power station in Dumfriesshire and the country's remaining two power plants, Hunterston B in North Ayrshire and Torness in East Lothian.

Dr Baker said: "Childhood leukaemia is a rare disease and nuclear sites are commonly found in rural areas, which means that sample sizes tend to be small.

"The advantage of carrying out a meta-analysis is that it enables us to draw together a number of studies that have employed common methods and draw wider conclusions."

Dr Baker added: "It is also possible that there are environmental issues involved that we don't yet understand."