What plants do Railtrack (South Eastern) use to hold embankments together ?

South Eastern railway line once British rail has probably been a railway line for over 100 years. I expect when the line was first layed trees where planted to keep the soil on the banks together, because of the tree roots.

Other than that I doubt if any plants were planted. Over a hundred years or so just how many seeds have floated onto the railways?

Hundreds, thousands?, of miles of railway lines propogated by native plants.

This is just my opinion.

Try this link it might help. Has some photos.

http://blog.gardenersworld.com/2008/08/05/jas-weeds-railway-05082008/ 

Link for HLS post. With photo.

http://www.gardenorganic.org.uk/organicweeds/weed_information/weed.php?id=10

Funny thing I hate it in the garden but in one of the neglected flower beds next to one of the main roads in coventry there is a whole flower bed of the stuff and it looks really impressive how weird is that.

Oh no not the dreaded mares tail 
Isn't knot weed a "reportable menace" ?  (you know what I mean)

It wouldnt have been planted, and I suspect nothing else was either. I would think all the plants were volunteers. In the days of steam, fire on railway lines was such a hazard they used to burn off the vegetation as a control measure, it was called swaling.