From the BBC website regarding MI5 activities during World War 2:
A French woman, codenamed Agent Treasure, threatened to scupper a covert operation after she blamed the British secret service for the death of her pet dog Frisson. The pet was accidentally left behind in Gibraltar during an operation to get the spy back to London.
She is described in the papers as "exceptionally temperamental and troublesome" and a "wretched woman." In May 1944, a month before D-Day, Agent Treasure threatened to end her bogus reports to the Germans. MI5 officer Mary Sherer said she blamed them for the death of her dog.
After D-Day she was sacked and returned to France. But by then she had already achieved her mission - successfully encouraging the Germans to believe the D-Day landings would be at Calais.
The Times reporter Ben Macintyre has recently completed Double Cross: The True Story of the D-Day Spies, which relates the story of Agent Treasure and her MI5 handler Mary Sherer, amongst others. He is now producing a television programme on the same theme and, as part of this, has been interviewing those with connections to the chief protagonists of nearly 70 years ago.
Amongst these is local resident Prue Evill, one of Mary Sherer's nieces, and Prue spent an hour or more with Ben Macintyre in London recently for the programme. Although Mary never spoke of her MI5 duties, Prue was able to describe her character and to provide good background material on her life (they were reasonably close in age, Mary being only some 15 years older than Prue).
The programme will be broadcast on BBC 2 at 9 pm on Monday 9th July.