Returning officers are appointed by the local council, but their duties as returning officer are distinct from their duties as a council employee. They are highly trained and their duties are very strictly defined - you shall do this, you shall not do this, you must do it at this point and not at this and so on. If you've ever seen the results of British elections being announced you'll have seen them. Usually nondescript sober men who stand up and say "As the duly appointed returning officer for the district of wherever, I hereby give notice that..." Even what and how they say that is circumscribed by law.
Representatives of political parties have the right to be present at each stage of the verification and counting process and they are legally empowered to challenge any part of it. Such challenges MUST be accepted and suspect votes investigated. Such representatives can also challenge the decisions of the returning officer. His or her decisions are final, but if Representatives feel they are being grossly negligent and/or corrupt they can make formal complaints.
Because returning officers have to sign the official secrets act, if they are found to have been dishonest in the execution of their duties, they go to Gaol. No ifs, buts or whyfors.
By mistake on their part I meant if there was a mistake in the register, or if someone had checked the wrong name off. Duplicate votes would require more checking.
No system is perfect of course, but we dont have the gross abuses that Americans on these boards frequently assert the US electoral system suffers from.
Not that I care about British Elections but thank-you for enlightening me regarding the detailed enforcement of your electoral integrity.
As a matter of note American elections are carried out by States here, and thus you may say we have 50 different elections going on at the same time. Of which there is only gross abuses in a few states.
That is of course not counting the unavoidable abuses that is a direct result of Federal usurpation such as the 1993 Motor voter[fraud] act.