try disconnecting the battery for ten minutes then replacing it to see if that resets everything.
You say it ticks over OK , so that means it starts OK?
Presumably , then , it means it`s not the immobiliser but possibly the engine management system faulty somewhere.
Alternatively , if you are in a breakdown service (AA etc) call them out as these blokes know all the tricks to start any car.
Ask a question on Honest John...It`s where the motor trade provide free answers
http://htdig.honestjohn.co.uk/forum/post/?t=59828
There is a solution here to bypass the immobiliser
http://209.85.135.104/search?q=cache:PwIbIblFVFQJ:www.howtomendit.com/answers.php%3Fid%3D74265+peugeot+immobiliser+problem&hl=en&ct=clnk&cd=5&gl=uk&client=firefox-a
chris conway
June 2008