The way this one works is, in the count hall, people present include:
the Returning Officer (impartial effectively civil-servant)
"tellers", the people actually performing the count (ditto, and who are allowed to touch the ballot papers)
party representatives (i.e. the party-political bureaucrats who are Making Executive Decisions for the party, liaising with candidates, in charge of the party-political observers, etc)
the actual candidates from each party (usually, though if they were running just to make a point and have zero expectation of winning they'll sometimes just go to bed)
party-political observers (from each party as can be bothered, so up to ~5 per ward but more typically 2-4 per ward i.e. electoral district), who watch the people performing the count to ensure that each ballot ends up in the correct pile, and that each bundle of fifty votes actually contains fifty votes (in that you're less likely to have errors if you've got 5-6 people watching like a hawk and duplicating counting, which hopefully makes everything run more quickly and smoothly IN ADDITION to preventing perceptions or realities of bias)
Some Journalists, Probably (but they're usually up in a gallery where they get a broad overview but can't actually see specifics of any of the ballots)
Cambridge, which is where I've done this, has 14 electoral wards. During counts, each ward typically has one table with two tellers at it, processing one ballot box at a time. You will also at each such table have 2-4 party-political observers, who may or may not be the candidate, and if they're not the candidates you'll probably have a candidate pacing as well. (Not all wards get counted at the same time, depending on how long it takes to get all the ballot boxes in from polling stations and verified). Floating around the room you'll also have the party rep, politically neutral support staff, and the Returning Officer and their floating team.
When a teller picks up a ballot paper, unfolds it, and sorts it into the appropriate pile, they do so in such a way that every single party political observer can clearly see the mark made on the ballot. If they pick up two sheets at once by accident and don't notice, an observer will sing out and require that they be separated. If there's any ambiguity at all about the mark on the paper, it will in the first instance be noted by both the tellers and the party-political observers and set to one side to be considered in more detail Later (at this point, that's around 5 people who've seen it already).
Once the first pass has been made through the ballot boxes, unambiguous votes are bundled up (generally into stacks of 50). At this stage any ambiguous votes will get discussed in the first instance by the tellers and party-political observers: if it's simply the case that the ballot was marked with a single tick rather than a single cross, or no marks at all were made on the ballot paper, there's no need to involve anyone more senior, unless someone is being a right arse (because at this point all they're achieving is delaying proceedings to no useful purpose, when it's already gone midnight and many of the people in the room have been up since 5am).
If it's even a wee bit more complicated, party-political observers will call their party representatives over. If party representatives in consultation with their candidates aren't willing to go "yeah, that's a clear spoil with no clear preference marked" (unanimously -- and at this point that's another 4-10 people who've seen the ballot, though it's still the case that only the tellers are allowed to touch the paper), you get the Returning Officer involved to make a final determination, which can take Some Time. During this process, floating observers from the Electoral Commission might have swung by, and if it's a particularly entertaining spoil party-political observers are likely to have called over their colleagues having a lull in a different ward to have a laugh. (Again, it's gone midnight, a lot of us have been up and largely on our feet since 5am, we're going to be keeping going for another couple of hours and then after that we're all going to pile into someone's living room for the afterparty.)
So: no, it's not that someone besides the voting supervisors will read the essay -- it's just that the voting supervisors consist of a wide array of people, to the point that an essay on a ballot paper is likely to be read or at least skimmed by getting on for 20 people (including candidates, party representatives, and politically neutral observers) even if it's not sufficiently amusing that others get called over Just To Have A Look. Basically the only people in the hall who don't have the option of having a gander are the journalists.
tl;dr the electoral process in the UK has a really kind of impressive amount of oversight at all levels and I feel very strongly about it. <3 This summary's not necessarily entirely accurate, not least because it has actually been about a decade since I was active in the process, but I think it gives the flavour!
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So.
The way this one works is, in the count hall, people present include:
Cambridge, which is where I've done this, has 14 electoral wards. During counts, each ward typically has one table with two tellers at it, processing one ballot box at a time. You will also at each such table have 2-4 party-political observers, who may or may not be the candidate, and if they're not the candidates you'll probably have a candidate pacing as well. (Not all wards get counted at the same time, depending on how long it takes to get all the ballot boxes in from polling stations and verified). Floating around the room you'll also have the party rep, politically neutral support staff, and the Returning Officer and their floating team.
When a teller picks up a ballot paper, unfolds it, and sorts it into the appropriate pile, they do so in such a way that every single party political observer can clearly see the mark made on the ballot. If they pick up two sheets at once by accident and don't notice, an observer will sing out and require that they be separated. If there's any ambiguity at all about the mark on the paper, it will in the first instance be noted by both the tellers and the party-political observers and set to one side to be considered in more detail Later (at this point, that's around 5 people who've seen it already).
Once the first pass has been made through the ballot boxes, unambiguous votes are bundled up (generally into stacks of 50). At this stage any ambiguous votes will get discussed in the first instance by the tellers and party-political observers: if it's simply the case that the ballot was marked with a single tick rather than a single cross, or no marks at all were made on the ballot paper, there's no need to involve anyone more senior, unless someone is being a right arse (because at this point all they're achieving is delaying proceedings to no useful purpose, when it's already gone midnight and many of the people in the room have been up since 5am).
If it's even a wee bit more complicated, party-political observers will call their party representatives over. If party representatives in consultation with their candidates aren't willing to go "yeah, that's a clear spoil with no clear preference marked" (unanimously -- and at this point that's another 4-10 people who've seen the ballot, though it's still the case that only the tellers are allowed to touch the paper), you get the Returning Officer involved to make a final determination, which can take Some Time. During this process, floating observers from the Electoral Commission might have swung by, and if it's a particularly entertaining spoil party-political observers are likely to have called over their colleagues having a lull in a different ward to have a laugh. (Again, it's gone midnight, a lot of us have been up and largely on our feet since 5am, we're going to be keeping going for another couple of hours and then after that we're all going to pile into someone's living room for the afterparty.)
So: no, it's not that someone besides the voting supervisors will read the essay -- it's just that the voting supervisors consist of a wide array of people, to the point that an essay on a ballot paper is likely to be read or at least skimmed by getting on for 20 people (including candidates, party representatives, and politically neutral observers) even if it's not sufficiently amusing that others get called over Just To Have A Look. Basically the only people in the hall who don't have the option of having a gander are the journalists.
tl;dr the electoral process in the UK has a really kind of impressive amount of oversight at all levels and I feel very strongly about it. <3 This summary's not necessarily entirely accurate, not least because it has actually been about a decade since I was active in the process, but I think it gives the flavour!