The equivalent system in the Buccaneer was going through testing, anyway they wanted to avoid damaging the expensive targets which were designed to imitate the radar signature of a Smerlov cruiser as that was the original primary target, although you could target offset radar nav points etc. So a 400 yard error was programmed into the test aircrafts' nav attack systems. Interestingly this led to a number of direct hits, so after a bit of head scratching the boffins from Ferranti just plugged the 400 yard fudge into all the aircraft!
Another point of interest, well to me at least, the Sea Vixen and Lightning weapons systems had a similar set up, where by the pilot would press the 'fire' button but it actually worked as a commit button in that it gave the system permission to fire allowing the computer to release the weapon when it reached the optimum launch point. Of course the difference was it was for the A/A weapons system which for the Vixen at least meant you could only launch Red Top/Firestreak if the computer wanted to, which may explain why a couple of rocket pods were the weapon of choice against a MiG-21 according to the Tactics Manual!