New laptop/computer
@WallFlower26 I looked at Amazon U.K., Currys, Overclockers, and CyberpowerPC U.K. The last two sell custom builds, so you can add or subtract features to try to stay within your budget. Currys doesn't have a whole lot of options, at least in the entry-level gaming PC category, and Amazon is a huge headache to search. Still, on both sites, the models with an Nvidia 1050 2 GB, which is still not quite enough for ultra settings if you have all packs installed, start at £550.
With Overclockers and Cyberpower, I started with the cheapest model that would support a decent graphics card and added that. Even with no other additions and the cheapest possible case, this model from Overclockers would cost £556. The cheapest card available, an AMD Radeon RX 570, is equivalent to an Nvidia 1060 3 GB; both cards are right on the edge of what could be expected to run TS4 on ultra for its entire run. The processor, an AMD 2200G, isn't great but should be fine if you don't do anything else while playing TS4.
Cyberpower is a bit trickier because it has more models, but not all of them support the graphics card you'd need. This model, with a Radeon 560 (equivalent to an Nvidia 1050 ti), the cheapest 8 GB RAM option, and no other upgrades, would cost £495 including VAT.
https://www.cyberpowersystem.co.uk/system/AM4-Ryzen-3-Gaming-PC-Configurator
But you'd really need to upgrade the power supply; the cheapest option is +£14. Other upgrades I'd recommend, if you could manage, would be the next processor up for £5 extra, and the AMD 570 8 GB graphics card, for an extra £20. (You could also play with the storage options, but it wouldn't save you much money.) With the VAT added in, this configuration would cost you £542, again with no monitor.
These are the cheapest laptops I could find when I looked a week ago, on Currys (sold out of this model, otherwise £580) and Amazon (£600).
https://www.amazon.co.uk/ASUS-FX505DY-BQ008T-Bezel-Gaming-Laptop/dp/B07MWD7SNN?th=1
When looking for computers, it's really just a matter of knowing what kind of hardware is required for its indended purpose, in this case playing TS4 on the highest settings. Any card weaker than an Nvidia 1050 or an AMD 560 won't be enough for the game. Processors are a bit harder to judge sometimes, but anything new that doesn't have a U or Y in its product number will be fine. (Some of the strongest U-series processors might be fine, if you can find one with a proper graphics card.) RAM is easy: get at least 8 GB. But if you compromise any more than that, you're not going to be able to play the way you want, and you may end up looking for another upgrade in a year or two.
