London Buses route 423 is a Transport for London contracted bus route in London, England. Running between Hounslow and Heathrow Terminal 5, it is operated by London United.
Route 423 was introduced on 22 March 2008 to coincide with the opening of Terminal 5 at Heathrow Airport.
It was an extension of route H23, that operated from Hounslow Bus Station to Hatton Cross Station.
Route 423 initally used Plaxton Pointer 2 bodied Dennis Dart SLFs from 2008 until 2011.
On 12 February 2011, the Plaxton Pointer 2 bodied Dennis Dart SLFs were replaced by Alexander Dennis Enviro 200 Darts.
- Hounslow Bus Station
- Hounslow Heath
- Beavers Farm Estate
- Hatton Cross Station
- Harlington Corner
- Heathrow Airport North
- Heathrow Terminal 5