A passenger who breaches Byelaws 1, 9, or 18 is by definition not “going about their lawful business”.
Byelaw 1 said:
1. Queuing
- an operator or an authorised person may require any person to queue in order to regulate order or safety on or near the railway.
- any person directed by a notice to queue, or when asked to queue by an authorised person, shall join the rear of the queue and obey the reasonable instructions of any authorised person regulating the queue.
1.1 The crowd waiting (for the photos testify that it is not a queue at all) at Stansted is clearly nothing to do with safety. There could be an argument that it regulates order, but it's at least as easy to make the argument that it creates disorder.
1.2 The fact that the crowd waiting has no identifiable end that you could be directed to join is clear proof that it is not a queue at all, and because it's not a queue this provision can't be applied.
If the crowd was a queue, then the instruction to join it is subject to a reasonablness test. This is subjective, but I can't see a lawyer wanting to get involved in any argument where there was a reasonable (pun intended) argument that it applied. Not surprisingly I can't find a definition of reasonable in terms of railway byelaws, and there are different tests applied in relation to other laws where the term comes up. Perhaps the most favourable might be "what would a reasonable person of ordinary prudence have done in the situation"? (So if you start a rebellion then you're well on your way to being in the clear because it's not just you).
In other areas of review of decisions of public authorities the test is quite firmly and intentionally biased in favour of the official "so unreasonable that no reasonable authority could ever have come to it". After 5 mins I think you can have a fair go at that, and after 10 mins I'd feel quite comfortable doing so.
Byelaw 9 said:
2. where the entrance to or exit from any platform or station is via a manned or an automatic ticket barrier no person shall enter or leave the station, except with permission from an authorised person, without passing through the barrier in the correct manner
4. where there is a notice by an entrance or exit on any part of the railway indicating that it shall be used for entrance or exit only, no person shall enter by the exit or leave by the entrance.
These appear to be the relevant provisions to people standing by a tensabarrier rather than a ticket gate.
2 is difficult to breach because walking past someone isn't climbing over or forcing through anything.
4 is useful to note; because it makes walking past the queueless exist harder to defend than asserting a path through the crowd. However as there are conflicting signs from the days when everything was an exit I can't see them wanting to try and enforce that unless they cover them up.
Byelaw 18 said:
8. Ticketless travel in non-compulsory ticket areas
2. a person shall hand over his ticket for inspection and verification of validity when asked to do so by an authorised person
This is quiet easy to deal with by holding a ticket out prominantly while walking (and if they say "Stop" then that's not the same as ask to inspect a ticket and verify the validity of it). If they do ask to inspect it then that can be fulfilled by handing over the ticket and continuing walking, or if they refuse to take it by dropping it on the ground in front of them and continuing walking (a better or worse idea depending on whether the method of purchase gives you proof you had it).
I'm taking from this a new confidence if I do need to go through Stansted again, but I'll buy the ticket online and pick it up from a ticket machine so I have proof I did have the ticket, and if I decide I'm at my waiting limit I'll try and take a photo of it that includes the crowd and can identify the station.
On Tuesday though I'm just taking the coach, cos that's just less hassle annoyance and worry.