70's Westmorland Comet Caravan

If it has all it's original internal fittings it's worth more than a pretty penny. They are highly collectible. They're also bloody heavy and designed for full time living, I wouldn't want to go touring with one.
The companies building these motto was you could have anything you wanted for a price. It wasn't unusual for a fully loaded Vickers to cost more than a decent house.

Something else to remember is traditional travelers vans tend to be dry vans ie no toilet/ shower onboard.
Personally I absolutely love them and if I had space to keep it and a TK Bedford to tow it I would have one without a second thought, the earlier Star version with all the cut glass windows and internal glazing along with the blue art deco stove would do me fine. I would even go as far as polishing up a couple of milk churns to sit outside the door.

The more caravans travel the more they flex and the more they are likely to suffer damp ingress. It's all fixable but for heaven's sakes don't ever be tempted to go shabby chic with one.

I'm not surprised Facebook went mental, I bet you had a couple of 100 people offer the top of the estimated sale price to pull it from the auction!
Unless I'm missing a lot of damage to the fittings or obvious rot or damp as I'm only looking on a phone screen No way is that only going to make £1000-1500.
I would guess it will go for nearer £6k potentially more in today's market. The last Westmorland Star (which is a bit more desirable IMO) I saw before COVID made £10k in apparently similar condition.

Personally I would advertise the forthcoming sale on Facebook pages like dragon sell or trailers and chalets for sale to increase interest, there's a few UK showman's groups around as well.