Hi Andylowe, Just a couple of points I think you should check out before blaming the immobiliser.
Have your battery tested after it has been fully charged - some companies (the likes of Quik-fit, etc) will do a load test free of charge. Reading with a multimeter only gives a passive read-out and does not give the potential voltage or current under load.
Have you checked the voltage across the battery when the engine is running ***8211; it should read 13.5 to 14.8 volts when engine running at 2000+ revs ***8211; this measures the out put voltage of the alternator.
When you checked residual voltage did you disconnect the battery ***8211; lock the car let it sit for 2-3 minutes ***8211; disconnect the battery positive lead and using the ampage setting on your multimeter measure the reading.
When locked the car should only be drawing enough current to maintain the memory in the
and the radio or Sat-nav if fitted. As a precaution I would disconnect the radio and see what happens. I had a similar problem some time ago where the radio was faulty and was drawing excess current even when switched off. Doing this would eliminate any radio problems and help narrow the search. The residual current reading of 1.7 amps is far too high and would drain even the best of batteries. Good luck in your search.
P.S. A duff alternator can also drain a battery!