Chris Brady writes
The Local Heathrow Express, which local residents were lead to believe
would also provide local services after all of the noise, dirt and
disruption which was caused when the HEX line was being built, never
actually eventuated. It MAY be introduced in the near future, but most
likely at prices well beyond most airport workers wages.

BAA have now ordered the trains needed for the new service.

"Siemens has won a contract to supply four new Desiro electric trains as
part of a GBP30 million investment by BAA, the world's leading airport
company, to provide a new stopping service between London Paddington
Station and Heathrow Airport. The new service will call at Ealing
Broadway, West Ealing, Hanwell, Southall and Hayes.
[...]
"The new trains are due to enter passenger service from December 2004."

http://www.siemens.co.uk/default.asp?content_id=2967

--
Dave