Vertex Allproof (1954) - anybody know about this watch type?

https://www.mikrolisk.de/show.php?site=280

It looks like a Swiss brand that concentrated on the British market.

I think they're originally British rather than Swiss, I've seen an interview with the current owner where he says he is the grandson or great grandson of the original owner

They formed in 1912 and supplied watches to the British Military during the First World War, but actually have a history before that as they began life as Dreadnaught Watches at the turn of the century. They are a lovely brand, excellently made - solid cases and Swiss movements. Very popular on the second hand market, they do command a decent price for good versions. Vertex are one of the Dirty Dozen, and also one of the 20 brands who supplied A.T.P. watches. 

They are British - they re-cased Swiss movements in Hatton Garden, London, but also had facilities in La Chaux de Fonds. Pop the back and you can find out the movement / ebauche, but I have known them to use FHF and Revue movements.

The current iteration of the brand is owned by the original family, but they have technically been closed from around 1970s until a few years ago. The new watches are interesting, and do refer back to the army watches they made, including some of the models that never made it to market (like the single pusher). 

Thank you for these replies. I can't sell the watch for obvious reasons. Any views on the strap - likely to be original or an addition? I am thinking of determining the gold content, selling the strap and buying a leather (gold isn't my thing)

The band is clearly marked "Montal Rolled Gold" around the springbar area. I'd assume that marking to be a very strong hint that it was aftermarket.

Purely from googling:

...Montal Watch Fittings Ltd., a company known for producing watch cases and metal watch straps. Montal Watch Fittings was founded in Birmingham, UK in 1942, moved to Cheltenham after the Birmingham Blitz, and was finally liquidated in 2010. 

https://mroatman.wixsite.com/watches-of-the-ussr/montal

^ this (thank you @OscarKlosoff for the deep dive)

However… whilst you have an all British affair here, the beads of rice bracelet may even have been sold with the watch as an add-on. As I say the watches were Swiss ebauches/movements re-cased in Hatton Garden or La Chaux de Fonds, so Montal may have also supplied the case as well for this exercise. It might have been customised a little if this is a presentation watch for long service. I would advise against getting rid of the strap as it’s in very good condition - by all means get a leather strap if you prefer but do not get rid of that strap as it turns the watch into something incredibly classy.

I assume you don’t have a box, papers or receipts… regardless the watch seems to be in very nice condition (the dial has very little patina), as is the bracelet, so it’s likely it hasn’t seen much wrist time. It’s superb - I would quite happily grab something like that if I was actively in the market for a 50s British/Swiss-jobber dress watch.