From the Langley school website, there are probably two coach services. Paly coaches told me on the tel last year that they had a stop at the Greenford roundabout at 7:30 am. I tried to get them to send me further information about the coach route so we could figure the best arrangement for us (if we are offered a place), but no luck. There is now a second coach service called Dhillons which seems to have stops in the Southall/ Hayes area.
My information is based on what I could find from various sources, I think a current parent with child at Langley/ Slough may know better.
If there are sufficient pick ups from Wembley/ Harrow areas, I would imagine one of the coach services may be willing to have an additional stop or the parents could get together and hire a minibus or some other method. It seems to me it would most times take an hour minimum each way. Hope I'm wrong!!