student,
There have been many before you who have asked similar questions. Stand by for a torrent of abuse about not being the right sort of character to be a mil pilot if you are already thinking about going civvy. The mil lifestyle is such that to get to the point where you become 'useful' to a civvy company, either fixed wing or rotary, means a significant personal and professional commitment to whichever service you join. In other words dont even consider joining if your actual reason is to get free flying training before jumping ship...it simply doesn't work like that.
With regards to SAR, RN pilots have generally done a number of years 'front line' before being given a SAR tour. Some might then manage to stay SAR for a while, others will just do 2-3 years before returning to other duties. Post 2012 when SAR-H starts to take hold the numbers of mil pilots in SAR will be massively reduced. You can work it out for yourself but the chances of new mil pilots getting in will be equally massively reduced as the old boys who for whatever reason are not transfering to the new company will be hanging on in there.
Good luck and if you succeed in your ambition to fly for the RN you will be joining a fantastic family - you just need to make sure you join with the right attitude and expectations otherwise you may find fitting into the family more difficult.
