If we are talking collapse of civilization, surviving in the UK, collecting food & staying away from other survivors, then we need to know what we are using an airgun for.
Hunting for small game? - Yes
Self-defence? - No, unless absolutely forced to (no better weapon available).
So, we want an airgun to hunt small game/birds & that is it. FAC, no not really. It isn't needed & FAC guns are going to have reduced parts lifespan due to the strain induced by producing more power.
12 ft lbs is plenty for small game, rabbits, squirrel, pheasant, Hare, pigeon, water fowl etc. All are easily taken by 12ftlbs air rifles.
One of the main survival considerations with gear is weight. More weight means more energy expenditure. If you can achieve a result with less weight, do it.
The HW80, TX range & other equivalent weight guns are just heavy. You can hunt just as effectively with lighter rifles & save valuable energy doing it & utilise the calories from the food you catch effectively.
This also applies to ammunition. 177 is the only calibre for survival airgun, just as effective for hunting but much more ammo can be carried for the same weight.
FAC guns are also usually heavy, so not an option as avoiding the additional weight much is more valuable than an extra 10 - 15 yds range.
One of the main contributors to survival is efficient calorie management. The heavier your equipment the more calories you need to ingest. A gun that is 2lbs heavier than an equivalent performance but lighter rifle is a liability that could be the difference between surviving & not.
Survival often means avoiding other survivors in hostile areas. This means being quiet. The air rifle is perfect for this even without silencers. Hunting while staying undetected is easier with an airgun & also makes hunting easier by not scaring game/birds. An effective silencer is a bonus but not a necessity. Shotguns & powder burners are good hunting tools but are loud, the ideal is never attracting attention, shotguns & bullet guns are all well & good as long as the opposition don't have them as well. Evasion is always favoured & hunting with an airgun helps maintain that elusiveness.
Reliability - any equipment taken needs to be rugged, simple & uncompleted mechanically, easy to maintain & easy to repair. PCP's, CO2, & pump ups are totally unsuited to survival, even if recharging air/CO2 was possible, seals will degrade much faster than a spring guns parts.
So given the above, which rifle meets those criteria. For me it has to be the Webley Excel. Vulcan is also good but the Excel is superior.
177 carbine barreled Excel. Compact, lightweight, rugged & accurate enough.
The Excel weighs 7lbs, less for carbine variant. Compare that to an HW80 or HW77, TX200 etc.
Simplicity - the Excel is extremely simple to strip down & rebuild. 4 screws, 2 pins, remove trigger & trigger spring. No spring compressor needed.
Trigger is basic, with a simple coil spring that is easily replaced. Sear spring is simple to fabricate if needed. Maintenance is therefore simple as well.
Barrel pivot, end plug pin & detent bar all simple pins, no screws so easy to make replacements. No fragile barrel shims or complicated breech lock up catches. Underlevers are a total no-no. To heavy & over complicated. Excel has a rugged, simple one piece cocking lever & simple but hard wearing barrel detente lock up. Proven 100% reliable over 30+ years, no gaulling, barrel droop etc
Accuracy - in 177 Excel is easily capable of hunting shots out to 30yds.
Open sights are rugged & simple. Fit a decent but simple & rugged 4 x 32 & you have a good sighting set up with back up opens.
The Vulcan derived guns are time proven, well engineered, tough & reliable airguns & are pretty much the perfect survival air rifle.
Take 2 spare mainsprings, a spare set of trigger parts, couple of piston & breech seals & a Swiss army knife & you have all you need for years of hunting. Only restricted by how much ammo you can carry.
If you understand exactly what you are expecting from your air rifle in a survival situation & more importantly what you do not require from it, then it becomes very clear that rifles like the HW80 are not the answer. KISS applies, along with less weight the better. Does your gun need to look cool? No, it does not. It needs to work & that's it.