Sorry to go off-topic for a mo, but the latent gricer in me wants to ask: I thought the HS1 went at Eurostar speed?
For the bit up to Ashford, it's on normal train lines (running parallel to the Eurostar line) which they have to share with the Victoria/Charing Cross trains. After Ashford, it then hops onto the Eurostar line and speeds up. After googling, it seems they don't allow it to do more than 140 mph.
This isn't as bad as the so called other High Speed services that Southeastern run, which aren't high speed. These run from St Pancras via Faversham and Ramsgate and then down to Ashford. Most of that is normal line, and coming back to St Pancras, as they have to slot in between the conventional trains running to Victoria on the stretch to Rochester, they're really slow, and so it's only once they get to Ebbsfleet that they then get onto the Eurostar track. Having said that, overall, they're still faster than the services they replaced.
PS I am not a train spotter, it's just having been on them a bit, you get to realise what's going on.