Citroen relay lgv immobiliser- how to bypass?

Out of the blue, citroen relay 1000D lgv (1999) immobiliser seems to have activated itself, (yellow light flashing 'code' on dash) the red 'master' key it turns out has no battery or chip in it so not sure how to bypass it as this was the only key bar the door key that I was given when I got the van second hand. Is there anything I can do that doesn't involve squillions at a citroen dealer? Thanks a lot for any advice.

Claire Tomlin
October 2007