Back in 2018 I was in one of the tower blocks overlooking Stratford International (so had a view of HS1) when what I thought was a path for the IRIS 320 was on RTT and was running. What actually appeared was a standard Network Rail test train, only with a pair of Eurotunnel Krupps in place of the more common 37 - the 37 had been left at Dollands Moor as opposed to remaining on the rake and being dragged by the Krupps. So I don't think the IRIS 320 covers HS1 anymore. It does still cover the Channel Tunnel though so will still make appearances in the UK at Dollands Moor, but as workings that remain entirely on Eurotunnel infrastructure they're unlikely to appear on RTT.