I have been advised by a couple of schools "subject to your hours" you may not have to do the whole IR. All you have to do is pass the flight test with a CAA examiner, of course you need to be up to standard and the training to get you there would be as required. The aircraft could then be say a Baron, or Duchess, for example.
You already need to have an ATPL then pass the JAR examinations, sit a GFT flight test with a CAA examiner and then do the IR as stated above. How much will this cost??????
A light twin would go for about 500 pound per hour?. I am not quite sure, some of the UK pilots may be able to help there. You would need about 1 hour for the GFT and lets say up to 5 or 10 hours for the IR.
Good Luck.