I can't imagine that David Cameron is going to pardon this and 'make a mockery' of both the British Navy and the OSA.

This is not my opinion I hasten to add, but the British government tends to be pretty militant when it cones to this kind of thing. The OSA is treated as 'sacrosanct'.

The ex-MI5 officer David Shayler had a similar situation, when he released the information about the state sponsored assassination attempt on Libya's Gadaffi: http://en.wikipedia.org/wiki/David_Shayler

   At the trial Shayler represented himself, claiming that
   the Official Secrets Act was incompatible with the Human 
   Rights Act and that it was not a crime to report a crime 
   although these arguments were dismissed by the court with 
   the latter being ruled irrelevant. Shayler's defence 
   attempted to argue that there were no other avenues to 
   pursue his concerns with the service and its performance. 
   The judge ruled that while this was true it was irrelevant.
   The judge instructed the jury to return a guilty verdict 
   and that the House of Lords had ruled in another case that 
   a defendant could not argue that he had revealed information 
   in the public interest. After more than three hours of 
   deliberation the jury found him guilty.

   In November 2002 he was sentenced to 6 months in prison, 
   of which he served three weeks in Belmarsh prison and just 
   under five weeks in Ford Open Prison, with the four months 
   served on remand in France being taken into consideration.