Cheers Chris, I thought they had something at the same point on the GU as Packet Boat Marina, if you look at their locations section on their website it mentions it but it looks like the same place.
Strictly speaking it probably is - but I don't want to get wet feet!
ta, that's a useful link that I'd found before but overlooked until you reminded me.
Also, thanks to MoominPapa, Bonganbiru, Saltysplash (will look out for that chippy next time I'm there) and Wrigglefingers for the first or close to first hand experiences - I'll be seriously considering High Line. One thing I have noticed from Google Earth is that a lot of the boats moored there seem to be doubled up, how does this work on a practical level.
Anyone got any recommendations for anywhere further south? What's the Thames like - expensive?