I was doing the same search some time ago and the final contenders were:

Lenovo t460 (or t460p) Asus UX305A Dell XPS 13 Dev Edition

However I ended up not buying any of those.

I had bought a toshiba i3 with 8 gb of ram 2 years ago for £300 and I didn't felt like any of those laptops would give an improvement worth the price.

Laptopts are a little bit stuck it seems. I sincerely tried to buy one but just couldn't justify... I am running Ubuntu 16.04 perfectly, everything just works.