[AngusH]

High speed 1 in the UK Section 2: https://en.wikipedia.org/wiki/High_Speed_1

Section 2 finished in 2007 (just within your 20 year cutoff!) It links the channel tunnel with London St Pancras. Much of the London part is in tunnels and it is 100% grade separated.

The uk High Speed 2 route was also going to do this and build a new high speed rail line and station into London, but the exact issues you describe seem to mean that it will be halting at a point outside London instead possibly using existing tracks.

Overall though, High speed rail doesn't need new tracks into cities unless all the existing lines are full (or they are too slow)

It's much easier to build high speed line in the countryside and link it to the existing lines that run to existing stations in cities.

(Also the Elizabeth line in London, but's more like a metro really, even if it is 'heavy' rail)

[noirbot]

That's good to hear! I suppose some of the sale for it is that the tunnel was already done, so the value was very clear. People were already taking that train on a slower version for business/tourism, so there was obvious value to be made expanding it.

Though, somewhat funny to me that it seems like it all got paid for by Canadian pensions?

[lmm]

You need an investor that's looking for something that will pay off over a long time period. Big pension funds are a natural fit. And the UK and Canada have a good relationship and a history of rail-related cooperation (e.g. a lot of UK trains are made by Bombardier).