Interesting point of law, isn't it ? A lot of laws were written & others made through judgement (becoming precedent in UK law) a long time ago and have not been changed in line with enormous changes in our working environment. I agree with the difficulty in parking a 777 (say) under Marshaler's (sorry, no spell check & everyway I try it, it looks wrong). Maybe the Law should be clear and hand over "joint" responsibility, to the Captain and the Marshaler. Any incident could then be directed at the one making the error.
In the days when these lovely swept back wings with winglets came into being, My Company had an incident where our aircraft, at LHR, taxying out, correctly positioned on the centreline, thumped another aircraft, in the tail. The latter was NOT correctly parked.Company hearing ruled against our Captain & we were all reminded of our "ultimate" responsibilities !!
Heady job really, eh ? Give the FO a leg & he screws up the landing, WE get the blame !! Maybe this is why we get these HUGE salaries !