There is so much out there nowadays. Look at the UKPK, yes, and also the Stretch version of it.
Couple of months ago I'd have said get a German Eye 4 1/4" stockman, but Eye have closed down. Then I'd have said get a Moore Maker stockman of similar size, but Queen, who made them, have also closed down. So, now I'd say see if you can find a Great Eastern #81 stockman. It's burly, so you might also like to look at GEC's finer #82 or Boker's current yellow bone stockman in C75. The Case XX sowbelly stockman in CV is very good, and affordable also ... there's a single blade, yellow delrin version of this too.
I have read a lot of nice things about the Kizer Vagnino, and Boker make a number of '42' knives .. some of which are a little long, so care there. The true answer to your question is the Boker Slack, a slim masterwork in VG10, but past 3" in the blade ... and now I have been to check a detail about it, I discover Boker have released another beezer; the A2 Mini which, I should imagine, after a perfunctory struggle with my conscience, I will own soon enough ... but it is a locker, so really rather off topic
.... Oh! Hang on. Forget all that and buy a Great Eastern Bullnose #71. Epic little knife. There is still a few around. Try DLT for a start.
1095 steel and orange delrin, or, as here, muslin micarta for dollars 55
https://www.dlttrading.com/great-eastern-farm-field-71-bull-nose-muslin-micarta-424
Knifemaker Shing has made some robust and pretty impressively engineered slipjoints in the past few years. Various sizes and styles but these are handmade, individual pieces of particular merit, and not cheap.
Also, look here:
https://www.heinnie.com/knives-and-tools/uk-friendly-carry-knives. The Manly Wasp on page 5 is a corking, repeat, a corking good knife.
Especially the S90V version ... very affordable for what's on the plate. The Benchmade Proper also has many virtues (it's price isn't among them though)
For its marlin spike, the John Nowill Navy knife is excellently excellent and endlessly useful. I like it a lot. Lighter than the British Army thing, though you may want to fettle the edge on it. You might look at the small Douk Douk as a possibility but don't buy the Svord Peasant, no matter what people say to convince you, or anything by Arthur Wright or Rough Rider. These have some qualities, but you will want something better almost immediately. Otter (Germany) and Joker (Spain) make some very good, affordable carbon steel folding pieces but sadly, although there are some highly recommendable and very, very appealing French regional knives, they tend to be a little bit over 3". If you can live with that, look for an Alpin.
Au Sabot make a good one
This could be costly. I rashly whetted several appetites for myself there
Oh yes, and the Enzo PK70 ..... have fun looking