Doesn't need to have amazing specs but a minimum is:-
Absolutely must be able to output 4K@60Hz via USB-C (or, at a push, HDMI)
8GB RAM minimum (16GB ideally)
256GB SSD minimum (and it must be an SSD, no HDD)
Able to run a 2-4GB Linux VM that has light usage, using something like Virtualbox
14" or 15" screen (don't want smaller or bigger)
Windows 10
£600 max
Acer Aspire 5 series is currently winning.
Can't find definitive proof that the Acer Aspire 5 can drive an external 4K monitor.
That will definitely 4K@60Hz via USB-C (my current work laptop is a T480 that I've got connected to the 4K monitor via USB-C), and the Lenovo's I've had over the years have been good.
No hurry to buy it yet, probably will pull the trigger by the end of Jan though, just in case I can get a slightly better model for the same, or less.
Can't find definitive proof that the Acer Aspire 5 can drive an external 4K monitor.
With that in mind I can see a refurbished Lenovo T470 with 16GB RAM, 512GB SSD, 14" screen and Windows 10 that is just under £600: https://www.laptopsdirect.co.uk/refurbished-lenovo-t470-core-i5-6300u-16gb-512gb-14-inch-windows-10-profess-t2-t470i516gb512gbw10p/version.asp
That will definitely 4K@60Hz via USB-C (my current work laptop is a T480 that I've got connected to the 4K monitor via USB-C), and the Lenovo's I've had over the years have been good.
No hurry to buy it yet, probably will pull the trigger by the end of Jan though, just in case I can get a slightly better model for the same, or less.