Online petitions don't do a damn thing in my view. More MPs with time in the service do more - in all parties. Stand for nomination at all levels - especially for local councils with military bases. To my mind Ashdown got far more attention because of his service record than his ability as a politician probably merited.
I note that in the US, most of the Democratic Congressional gains in the recent election
have been made by men with records in police, CIA, FBI or the Armed Forces who were specially sought out by Democratic recruiters (NYT, free reg required).