Development work? I assume you are a Computer Scientist/Programmer then and comfortable with cracking open a laptop up and doing upgrades?
I highly recommend a used/refurbished Lenovo ThinkPad from the T420 series upwards. They're old machines, but built like a tank and have wonderful keyboards with plenty of travel. Like I said, they're old, but they use the fully powered Intel processors from the 2nd Gen onwards rather than the crappy, low voltage versions that most laptops have these days. You can get one for about £300 max. Just chuck in an SSD, another RAM module and change the display out for an IPS one.
I also notice that you care about build quality. If that is your #1 priority then NOTHING beats a ThinkPad. The keyboard is spill-proof with drainage holes for water, and they have an internal rollcage for max. protection. I know some devs who still use ThinkPads from the old IBM days. Sort of shows how reliable/resilient they are.
I personally use a ThinkPad T440p and added in an SSD with Archlinux running on it. I also have a Dell Inspiron 17 5000 (the one that came out November 2016, so fairly new) and my ThinkPad T440p from 2014 smashes the Dell in terms of real-world performance.
Check out the /r/ThinkPad subreddit if you're interested.