anyone who's travelled the high road between Loch Long and Gare Loch can't fail to see how massive the collective facility at Coulport/Faslane really is, and how difficult it could be to remove it somewhere else. how much of an effect the base has on the economy of the area around Helensburgh is evidenced by it containing one of only a handful of Waitrose stores in Scotland, and comparing it with Greenock on the opposite side of the clyde, a similar distance out of Glasgow, is stark.
more likely the base would be used as a trade-off against a share of the national debt, or oil revenues/decommissioning costs.