On the Thames Estuary and hidden below the waves, reports BBC News, is one of London's most unlikely tourist destinations.

We've travelled about 30 minutes, along with a handful of day trippers from Southend, into the estuary.

Slowly, a set of masts sticking out from the grey waves come into view. This is the SS Richard Montgomery, beached on a sandbank in 1944.

The problem is that the wreck holds 1,400 tonnes of explosives - which could detonate.

The ship is decaying and if the cargo explodes, a huge tidal wave could blast towards the Kent and Essex shorelines and onwards towards the capital.

Richard Bain is from Jetstream Tours, which is seeing an increased interest in trips to see the masts of the SS Richard Montgomery.

For more on the wreck with an exclusion zone around it is located not far from shipping lanes using the Port of London.