Rosyth?
"Most worryingly, the NAO also pointed out "the lack of berthing space within the Devonport dockyard","
That could be a very big problem. After Scottish Independence (coming very soon) I doubt whether the Scots will be keen to keep England's radioactive junk, so they'll either end up paying a stonking annual rental bill for the berths, or will have to move the 6 subs down south somewhere. Lined up along the Embankment maybe?