EBay is your friend here. You can upgrade just about everything for the cost of that Nait50 - £2700 is a lot.
Olive 72/Hicap/ 250 is the classic combo for a good reason -as long as the latter 2 have been serviced in the last 12 or so years. The total cost of all those should be considerably less than for a Nait50.
If that is too many boxes, pick SN2 or SN3- the latter is better and has a decent MM phono stage built in.
You probably will need a new cartridge now or soon. A good MM probably beats most cheap MCs. LP12/ Ittok and the above amplification is good enough to show the merits of £2K+ of MC, but that doesn’t make it mandatory. There are good options below £500 from Audio Technica and Ortofon, and those might look the standard choices, but also consider Dynavector, Denon, Rega, Sumiko and Hana. Given the age of your cartridge, any of those should be a big help.
If you need one, a Dynavector P75 mk4 is a great value and very flexible phono stage, with phono boards or a Prefix as decent alternatives. I paid £400 on eBay.
That lot should sound appreciably better than the previous boxes did through your existing speakers. However, my guess is that you could improve on those speakers for a few hundred quid, though they are easier to place and drive than some options.
Small speakers? Linn Kans, Royd Edens, EPOS 11/14 or Neat Petite/ Motive 3? All are very different, but available for under £350. If you have a bit more space, several other options spring to mind. Speakers are very dependent on your ears/taste and room, but my guess is that any of those should sound a bit more exciting and involving than R852s.
If that lot has not spent all the available cash, spending some cash upgrading the LP12 may be well worth doing too. EBay / Pinkfish won’t deliver a cheap Karousel bearing, but a second-hand power supply might well be worthwhile for a few hundred (depending on what you have now), and you might even be able to look at a better sub-chassis.
If the LP12 sits on a bookcase or sideboard, and if you can do it, the best value upgrade of all may be spending £100 or so on a wall shelf.
You won’t need expensive interconnect or power cables (those that come in the box will be ok), but speaker cables can be worth thinking about. At least 3.5M long is recommended, and many people suggest strongly that 5M or more is better for sound quality.