Shingle Street: What REALLY Happened?

Shingle Street is a coastal hamlet in Suffolk, UK.
Strange events there during WWII have fueled big rumours ever since...of an actual German invasion attempt!
Anecotal evidence says along the beach may have been a pipeline defence system, which could release a flammable mix to set the sea on fire: such devices were tested in the UK but there're no records that they were used in this area.
However, official documents of what may/may not have happened at Shingle Street in those desperate days were locked up by the British Govt for 75 years - not the usual 50 (why?) - until questions in the House of Commons led to their premature release in 1993.
The story goes that a small invasion fleet of German E-boats landed troops at Shingle Street, the pipeline defence was activated...and many burnt bodies were later retrieved from the beach.
A 2002 BBC report suggested the invasion was a fake, manufactured by the British Head of Propaganda during the war, who may have spread rumours of a failed invasion to boost morale. If so, then they went to great lengths, as the Suffolk Home Guard received many reports of an incident resembling this at the time. It's also been suggested that the rumours, widely reported in the US press, were a successful example of black propaganda, aimed at ensuring American co-operation by showing that UK was capable of resisting the might of the German Army.
Whatever the reality, there are too many eye-witness accounts and sworn testimonies to deny something happened at Shingle Street in August 1940...

defensive pipeline testing, WWII: no location named...