I have been responding to these on Facebook but find myself typing the same thing over and over again. My view is that this the most meticulous conducted ballot I have witnessed.
Let me explain a few things. Parties to the election (those putting up candidates or in the case of this referendum campaign groups) appoint Polling Agents and Counting Agents. I was each for Scottish Greens (Yes) in Aberdeenshire. Across Scotland there were thousands for Yes and No groups plus there were international observers and observers from the Electoral Commission roaming about.
Inside each Polling Place (the building) are one or more Polling Stations. At each Polling Station there is one and only one ballot box. For this election each Polling Station served something less than 1000 people - at least in Aberdeenshire so widespread queues were unlikely.
Polling Agents can, if they wish, watch everything going on in the polling place from start to finish: They can turn up at 7am and check that the ballot box starts out empty. They can stand and watch every voter being issued with a ballot paper and putting it in the box. They can watch the box being sealed at the end of the day. And they can follow the van taking it to the count and watch it being unloaded. The boxes are accompanied with a small sack of paper - stubs of ballot papers, the marked register, etc - all the paperwork you'd have seen at a polling station.
It's unusual for anyone to actually do this. Usually Polling Agents dot in and out.
Polling Agents also check that there isn't anything in the Polling Place which shouldn't be - e.g. literature from the other side and that voters are not hassled by the opposition (tho that is strictly the job of the Presidening Officer and the Police).
Outside the Polling Place, you may find representatives of campaigns. They must stay out of the Polling Place while wearing/ displaying any propoganda and they shouldn't interfere with voters in any way. But they can ask people to identify themselves (you don't need to give this information) and can answer questions. If they are collecting details of who has voted, this is so that those people are not called upon later in the day to ask them to go and and vote (known as knocking up).
There is always more than one polling clerk/presiding officer at each polling place and they to some extent check up on each other. For anything to go wrong, here would need collusion of presiding officer, polling clerk and polling agents.
For postal votes, these are collected over a longer period and kept securely. Periodically, a batch is opened and the signatures checked against the application. Bundles of papers from that batch are then put in sealed ballot boxes to await the count. Counting Agents can turn up and watch all this.
The pictures of neat bundles of ballot papers being taken out of ballot boxes are these postal votes - all ready verified: a known number of papers in each box.
At the CountAt the Count, the paperwork is first checked and then the ballot box is opened and the number of papers inside checked against the number of ballot papers issued. Lots of the videos showing Yes being put under Noes are really this first verification count. Counting agents watch this process and you often see them making a tally of the ballot papers, If any box (and remember this is from a known location) has an unusual split of votes, the Counting Agents should notice at this point.
Counting agents will know the total number of ballots in each box - and hence the total number of votes cast if these are all added up.
Sometimes there aren't the same number in a box as was issued. But I've never seen a difference of more than one. Sometimes there is a polling card (the card telling people where to vote) in the box - perhaps someone took the ballot paper home by mistake.
The ballot papers are then put in one big pile and each station is given a known number to count. They then divide the papers into Yes, No and Dubious. The Counting Agents watch this and check that piles contain only Yes, No and Dubious. They may make a representation about where any individual paper should be put - but in case of doubt they go to Dubious. This is why is much easier if people just put a X in the box.
The total number of Yes, No and Dubious must match the number of papers the table was issued with. They will check and check until this is true. Counting Clerks sometimes flip throuugh bundles of votes just to do a quick visual check that they contain only Yes or only No - it's quite easy to spot a stray ballot of the other side as we are good at pattern recognition.
The Counting Agents will know how many Yes, No and Dubious come out of each table. They can add it all up to make sure it matches the total number of ballots.
Dubious votes are taken to the Returning Officer and they, in consultation with the chief representatives of the Counting Agents, decide whether these are spoilt (and for what reason), or whether they should count for Yes or No.
Fraud : Personation
At polling stations, the Presiding Officer and Polling Clerk, know who has been issued with a postal vote. So if these people attempt to vote in person, they known there is a problem. In case of a postal vote not reaching someone, the Returning Officer can issue a duplicate because the checks made on returning postal votes are through. But this is something that needs to be sorted out with the overall Returning Officer not at a polling station.
If someone is marked as having already voted and someone else turns up and tries to vote claiming they are that person, then a criminal offense may have been committed - called personation. The second person turning up will be held at the polling place and their identity checked. If they are who they say they are, they will be allowed to vote. And, because there is a number on the back of each ballot paper which is logged against each voter, the fraudulent ballot paper will be found and removed (for evidence!). Personation used to be common in Northern Ireland which is why ID is required to vote there. In the rest of the UK is it so rare that this check is not deemed necessary. I understand that 10 cases are under investiagation in Glasgow. Out of millions: that is tiny. With such a high turnout, personation will be detected. It is less likely to be detected in a low turnout election.
In the ideal would, the Polling Agent or Polling Clerks would be sufficiently embedded in the community to be able to say 'Hang on - you're not Debra Storr' and nab fraudsters before they vote. My local Polling Clerks know me, of course. This isn't easy with large populations. Returning Officers will use local people - and the same local people - as Polling Clerks. In small rural polling places, this informal verification works. In larger places, it can't : one reason why I prefer many small polling places.