A list can be found in the link below.
http://www.dft.gov.uk/pgr/rail/passenger/invitationtotender/

Quote :

"DfT Rail Procurement formerly had a settled policy to publish franchise Invitation to Tenders (ITTs) once the franchise has commenced and the Public Register Franchise Agreement (PRFA) has been agreed between the relevant Train Operating Company and DfT. Following a review of that policy, in future, subject to the application of any exemptions under the FOI Act (e.g. commercial prejudice), DfT Rail Procurement now intends to make ITTs publicly available at the same time as the ITT is disclosed to pre qualified bidders."