Honestly, at 27", I'd recommend a 1440p monitor. My second monitor is 1080p 25" and I notice a slight "screen door" effect on it, which is only going to be worse at 27". My older 1080p 24" monitor actually looked a bit better in that respect, so if you want to go 1080p, I'd say stick to 24" rather than 27". The 1080p 144Hz ASUS TUF Gaming VG249Q and 1080p 165Hz ViewSonic VX2418-P-MHD would be options for 24" monitors.
My primary monitor is a 1440p 170Hz Gigabyte M27Q, and I'm very happy with it, but that is much more expensive in the UK for some reason. I got mine for $320, which works out to only £226, but instead it's £340 right now on Amazon UK. There's also the 1440p 144Hz AOC Gaming CQ27G2 that I've heard good things about, which is £268 on Amazon UK, and the 1440p 144Hz ViewSonic VX2758-2KP-MHD, which should come in similarly priced to the AOC one, but seems to be sold out on Amazon UK.