THE Central line has been revealed to be the hottest Underground line, with temperatures soaring to 32C.

A map was compiled by Transport for London (TfL) on July 28 last year - the hottest day of the year - showing the warmest parts of the Underground.

It showed that the Central line, which runs through large parts of Waltham Forest and Redbridge, was significantly hotter than other lines, including the Jubilee line, which peaked at 25C.

The line reached its peak temperature between Holland Park and Mile End.

TfL has used temperature maps for years to help keep an eye temperatures on the Underground.

A TfL spokesman said: "Cooling the Tube is one of the greatest engineering challenges faced by London Underground (LU).

"It is a programme that will take years, not months, to deliver results."

The spokesman added that millions of pounds were being invested to deal with high temperatures across the Underground.

Initiatives include new air-conditioned trains, set to arrive on the Metropolitan Line from 2010, the Circle, Hammersmith and City lines from 2011 and District Line from 2013.