Hi Gents
Just my twopenneth worth...
I have PM'd a couple of jobs for London Underground and TfL.
Initially, a contractor needs to have been accredited via something called Link Up. Link-up is the UK rail industry supplier qualification scheme, providing a single common registration, qualification and audit process for suppliers that is shared by the UK rail industry - effectively if,as a contractor, you get through this process any one of the "buyers" from the rail industry know that you are employable. It is now quite a process and not cheap.
If you are yerning to work on the underground (can't thnk why!!!) you would need to establish contact with a Link Up approved contractor and apply for work through that route.
It is a tough tough marketplace, IMO the "buyers" are only interested in price and the surveyors are only interested in quality and we all know what happens when you pay peanuts!!!
If anyone wnats to PM me for a contact explaining what you are loking for I will respond ASAP.
Kind regards,
Brian - The Project Damager