The original 284 (introduced by Winchester in 1963) was intended to give 30-06 performance with a 150gn bullet in rifles with short actions, specifically pump and lever types. (It wasn't chambered in Winchester's model 70 on its launch.) As such it was rather limited by its COAL of 2.800" which sees most bullets that weigh above 140/150gn seated too deeply in the case. To get the case capacity / charges for the needed performance, Winchester made it a rebated rim design (0.473" as per the 308/30-06 etc to fit standard rifle bolts, but with a fatter body and - very unusually in '63 - 35-degree case shoulders which must have made it an expensive case to manufacture back then.
In 1963, it was a complete and utter commercial flop, especially as Winchester was caught flat-footed by Remington who'd introduced the 7mm Rem Magnum the previous year giving higher performance and much better suited to 160-175gn bullets. It seems that US elk etc hunters who wanted good 7mm performance were prepared to live with long-action bolt guns after all. Wildcatters loved the 284 case though and there was a continuous demand for its brass which Winchester made on an occasional basis for many years, probably still do, even though factory ammunition was dropped many years ago. AFAIK, nobody else ever produced any 284 ammo. After a very few years, Winchester dropped its two 284 Win rifles too.
Around the end of the last century, two developments moved the 284 on and stopped its slow but inevitable demise - the 6.5-284 Winchester wildcat became an increasingly popular long-range hunting and match cartridge in custom built rifles in the USA. Norma picked this up and introduced the 6.5-284 Norma cartridge in 1999 in a long action (over 3-inch COAL form). Around the same time, US magazines started to write about custom long-range 284 Win rifles whose chambers had been throated to allow sensible seating of heavy bullets. To differentiate such from the factory version, it was often unofficially renamed the 284 LT, or 284 Win LT (long throat). Allied to new slower burning powders, it proved to be an excellent performer.
Finally, match shooters especially in F-Class picked it up using (mostly) Lapua 6.5-284 Norma brass necked up, also in some slightly 'improved' versions such as the 7mm Shehane. It is an excellent 1,000 yard match cartridge in widespread use in the UK, USA, and British Commonwealth countries.
So, as a UK deer cartridge, it is a candidate for a custom rifle / rebarrelling job in any short-action rifle with a standard 0.473" bolt face if the user is willing to be restricted to 2.8 overall lengths and 140-150gn bullets (less for all-copper types), or in a standard long action for longer COALs and heavier bullets. In short-action form, it'll substantially outperform the 7mm-08 Remington, and should be a nice cartridge to shoot. As others have said though, in a long-action rifle it doesn't offer any advantage over 280 Rem and 7X64mm, in fact will have a bit less performance.
If anybody is contemplating a 284 custom job, one point to watch is that whilst most gunsmiths who build rifles have 284 chamber reamers, they are more often than not tight-neck jobs designed for match rifles and therefore need the case-necks turning down. They often have long freebore front-ends too that will cut an over-long throat for anybody wanting to use the cartridge in a short action.
The 284 is a fine cartridge and whilst Winchester brass is rarely seen, Norma or Lapua 6.5-284 Norma brass is widely available and very strong / good quality and easily enough expanded by 20 thou' to turn it into 284. Dies are readily available too.