It goes along the line which runs parallel with the Central Line, joining the GWML at Old Oak Common. The line via Greenford is used by Virgin for their blockade busters and was used by up FGW services when they diverted via the Chiltern Lines when Reading was closed.
And what's a blockade buster?
When the southern part of the WCML is blocked by engineering (most recently this Easter), Virgin start all their services from Rugby, and run an hourly shuttle known as the Blockade Buster calling EustonCoventryNuneaton, which is routed via Willesden, Ealing Broadway, Greenford, the Chiltern Mainline and Kenilworth.
This shuttle is a 3×221; quite a sight to behold when it stops at Coventry!
When the southern part of the WCML is blocked by engineering (most recently this Easter), Virgin start all their services from Rugby, and run an hourly shuttle known as the Blockade Buster calling EustonCoventryNuneaton, which is routed via Willesden, Ealing Broadway, Greenford, the Chiltern Mainline and Kenilworth.
This shuttle is a 3×221; quite a sight to behold when it stops at Coventry!