What hardware does your current desktop have?
Keep in mind that laptop graphics cards will tend to be significantly less powerful than the current desktop cards with similar model numbers, so don't expect performance on par with what you see in reviews for those cards. The laptop 3080 doesn't even use the same graphics chip as the desktop 3080. It uses a chip similar to that of a desktop 3070, with slightly more cores enabled, but at significantly lower clocks, and while the exact performance level will vary from one laptop to the next, don't expect a laptop 3080 to perform better than a desktop 3060 Ti.
A laptop 3070 tends to be a bit slower than a laptop 3080, but on average the difference tends to be much smaller than what is seen with the desktop parts, typically less than a 25% difference between the two going by the numbers I've seen, and in some games very little difference at all. Though again, that can vary based on how the laptop is designed, and what sort of power limit the graphics hardware is given.
In my opinion, it's probably not worth the £1000 difference, though the specifications tab isn't loading on those pages for me, so it's hard to tell the exact differences between the two systems. The one has a larger SSD, but that probably only accounts for a £100 difference or so. It has a 4K 120Hz screen as well, compared to the 1080p 300Hz screen on the other, though it sounds like you intend on using an external display anyway. Apparently neither is available for purchase quite yet, so there are likely no reviews of those exact units either, and it's difficult to say how availability might be, given the current GPU shortage.