Firstly I'll preface this by saying British conditions generally don't get that cold but Scotland can definitely have -20C and below winters. That said, as an ex long time Nordics resident with a fair bit of experience of cold temps I'll try to share some advice. Firstly, I'm not sure what your experience is like so forgive me if some of this is stating the obvious. Overall, camping at -30C really isn't much fun (in my opinion I'd rather go cabin to cabin) and is more about how you prepare and make sure you don't make many mistakes (losing gloves, for example, or 'personal care' mishaps) so make sure you've got your skills dialed in as well as your equipment. I'd always try to get a fire going as there is only so much your sleep system can do to stop you losing warmth, so prefer having an axe with me to split firewood which has pretty much replaced my laplander. I'd also calmly but seriously take a look at your insulation to the ground and figure out whether this needs to be beefed up or whether your intention is to use a portable tent stove/similar. Foot care is also paramount and I'd recommend bringing a couple of heat packs in case you get cold feet, there is very little you can do to actually warm them up once they become numb/damp otherwise, and changing socks due to perspiration should be a part of your day you never skip.
As for specific gear pieces, I'm a fan of mesh base layers as they avoid the clammy 'end of day' feeling which rapidly turns to feeling chilly. Montane Extreme salopettes are excellent (in high wind especially) but fairly useless for UK conditions unless you're ice climbing and stationary a lot, and although the Montane Extreme smock is a solid top piece, for -30 I'd want my North Face McMurdo with me instead. Boots I was told a couple of years back that Salomon Toundra Pros were the way to go for snow trips and they were right, they're fine to snow-shoe in but wouldn't fit a crampon with much comfort, however they are a lot better at walking in than insulated mountaineering boots which cause me significant foot fatigue. Gloves wise, I struggle keeping my hands warm in most conditions so I usually take an extra pair regardless of the season. For deep winter a full primaloft liner glove under hestra army insulated mittens works for me - and a set of oversized dachsteins in my pack in case I need to layer them together. Down booties for night time are something I once scoffed at but definitely proved useful in the past when I stupidly let my socks wet out.
The Scarp 2 is a solid all rounder, personally I like the Hilleberg Soulo and HMG Ultamid for winter use but I find winter gear very personal - depends on what you intend to do in the outdoors, how active you're going to be (pulled on a sled, high effort mountaineering, snow shoeing, etc) and also perhaps obviously your gear needs depend a lot on your circulation and metabolic rate. Some people carry more natural insulation whereas others pump out heat like a furnace regardless of the season. Also, importantly, it really isn't worth the investment unless you're serious about going out in all sorts of weather and doing it fairly often as well as have the constitution to put it all in a pack and lug it about.
Are there any specific objectives you're looking to do?