Julian,
Have to agree with Tom on this. Consider if the instrument on which you are relying to fly your ILS is on the outer limits of its tolerance, you are going to be a long way from the runway when you arrive at your DH.
I also remember the 'wicked' old CAFU instructor who conducted my IRE course flying an entire ILS half scale deflection off the centreline and doing nothing about it until a few seconds before we arrived at DH, explaining that the approach he had just flown was unacceptable because he had not attempted to fly with the needles in the centre and had made no attempt to recover on to the localiser.