For the most detail, you might want to hunt down a copy of BR's report on the different routes: "Rail Link Project: Comparison of Routes".
A copy is available at the British Library as well as some other University libraries.
Otherwise,
this case study on the CTRL will probably be of use too. Skip to page 79, "Route Options and Appraisal (1987-1993)". This includes content from BR's 1991 report as well as many others.
I just got a copy of the book from my university library and has the following interesting pieces of information:
The “final” route BR proposed in 1991 was to run the line towards the Medway, but cross it more downstream than how it is today. It would run to the South of Swanley where there would be a junction at a place called Bourne Wood for trains going to Waterloo. The line would then run aside the SEML to Hither Green into a tunnel.
It seems there wasn’t complete decision on where it’ll go next but Br wanted the line to swing west to Peckham to allow trains to reach the existing network at Warwick Gardens, although other connections were proposed at Elephant and Castle and New across Gate. The line would then continue under the City to Kings Cross Low Level.
There seems to be an awful lot of different NSE brands and I’m struggling to work out what they all mean. It speaks of a “Kent Express”, “Network Express” and “Thameslink Express”. The Network Express seems like a 1980s style Javelin train, although BR also wanted to route domestic CTRL onto Thameslink. Although they seemed to be rightly concerned about the loss of capacity on the Thameslink line.
Eurostar trains a day would have continued beyond London. Clearly this was the pre-Schengen/Single Market days.
As said before, Arup’s route, the one that got built, definitely intended to use the low level station for its terminus.
Wikipedia says the high speed networker train would be the class 341. But Chris Green’s “The Network South East Story” suggests that the class 371-a train built for Thameslink, would be 125 mph capable and thus be used on the CTRL. However I have a picture below from a 2011 Railway Magazine article that clearly shows some kind of high speed train but designated class 381, which Wikipedia seems to think was intended for several routes including LTS...? Looks a little overpowered for Southend services to me.
