The group, representing at least 50 children living in 720 homes along the cables' route through north-east London and Essex - South Woodford, Walthamstow, Chingford and Woodford Green - are to seek a judicial review of Mr Heseltine's failure to formulate regulations over the cable laying.
They maintain that he has not fulfilled his obligation under the Electricity Act 1989 to 'protect the public from danger arising from the generation, transmission or supply of electricity'.
But National Grid, which is laying the six 275,000V cables, says that it has strictly observed National Radiological Protection Board regulations that households should not be exposed to electromagnetic fields of more than 1,600 microtesla.
Martyn Day, the families' solicitor, claims that recent research from Sweden showed that some some childhood cancers occurred at up to six times the national average where a level of as low as 0.2 microtesla was found in homes.
It is a highly contentious subject among scientists, however, as other studies have failed to show any link.
John Washburn, a spokesman for National Grid, said that the studies were inconclusive and that the company had done all it could to reassure the families living in the area.
The DTI declined to comment.Reuse content