I know they are in Treknow, Cornwall but have no idea where that is in relation to London.
Looking at a map, its a long long way, more so on public transport. I recently spent some time with a son in London. Coming home, from Euston to Preston (240+ miles), 2 hours. The remaining 20 mile part was over an hour, including waiting for the connection.
In London, theres the Imperial War Museum, HMS Belfst, Cutty Sark, the Golden Hind replica, and the British Museum still has its charm. A trip on the Thames river bus is a must do.
For events, have a look on modelboatmayhem. They have an events section, and a strong UK bias, being a UK site.