If you’re looking at more technical wear, if it’s just light rain then for the UK temps you won’t need anything more than a decent fleece-lined windproof jacket with a DWR (water resistant) treatment... which can be reapplied in future once it wears off, or a mid to heavy weight fleece + a water resistant windbreaker if going the layers route. Layers offer more flexibility as far as using different weight fleeces for different temps (or none at all for going out when there’s a chance of spring showers etc) but obviously you need to try them together to make sure they fit together nicely. Always look at the mountaineering stuff though as anything snow sports carries the associated snow tax with little difference to show for it other than a lift-pass pocket, snow skirt or gaudy colours.
You can layer in a packable down gillet or jacket from Uniqlo or somewhere if it’s bizarrely cold like when we had that ‘Beast from the East’ a few years ago but normally the high levels of insulation you get with some of the more fancy technical jackets just isn’t needed, and if it’s only light rain then there’s no need for Goretex or any of the other layered waterproof membranes which cost a bomb.
Also side-note but re the fur post a few up from here... one of the reasons the proper expedition jackets use real fur is that it deals with the ice crystals that form in extreme cold very, very well - as the animals whose fur it belonged to live/evolved in the harsh conditions it’s designed to be worn in - versus the plastic-based faux-fur which just clumps up and loses it’s protective properties. That’s why it’s used. Entirely unnecessary if you’re not a Canadian in winter or the like, dealing with the kind of conditions that will kill you quickly if you’re not layered up properly though.