Temperatures on Tube trains can reach 30C

The company has received more than 3,000 proposals from all over the word since the competition was started in July by the Mayor of London Ken Livingstone.

One Israeli company suggested that giant snow making machines at street-level could help by pumping snow into containers placed in train tunnels or at platform entrances.

Then as trains pass through the network, it would create air currents causing cold air from the containers to circulate and cool passengers in stations.

London Underground has long grappled with the problem of how to reduce heat in the narrow tunnels - some built more than a century ago - which lie up to 60 metres below ground.

COOL IDEAS Your ideas to cool the Tube

Temperatures regularly top 30C (90F) in the deep tunnels of the network, according to a survey conducted by Liberal Democrat shadow transport minister Tom Brake last summer.

During this year's exceptionally hot summer, signs have been put up in stations warning passengers of the hazards of travelling in such temperatures and what they should do if they begin to feel unwell.

BBC News Online recently asked readers for their ideas on how to cool the Tube and more than 2,000 were sent in, which were passed to Ken Livingstone.

Among them were handing out ice-lollies, turning the Tube into a Venetian-style oasis and putting up posters of snowmen to make people think of winter.

The criteria for entries can be found on the Transport for London website.