I quite like this £200 27-inch gaming monitor
1440p, 165Hz, FreeSync/G-Sync and VESA support.
It's rare to see a 27-inch 1440p 165Hz gaming monitor for £200 or less, but that's exactly what you can get from X= on Amazon UK at the moment. This alphabet-soup-inspired model, the X= XRGB27WQ, uses an IPS panel to deliver its spec point of choice, with FreeSync/G-Sync support, a 2ms GtG response time and a clean, RGB-optional design.
This particular model hasn't made it to the review archives of RPS just yet, but I've tested it for Eurogamer and found it most agreeable, mostly on account of that spec sheet for the price. The actual design isn't bad, but the metal stand isn't height-adjustable and the styling isn't as impressive as more mainstream options. Still, there's a 100x100 VESA mount so you mount this on a monitor arm for an ergonomically superior option anyway.
The actual panel quality is solid though, with the only meaningful upgrade available being the LG Fast IPS panels available on more premium models, which boast a grey-to-grey response time of 1ms rather than 2ms. Unless you're a hugely competitive esportster (that would be better served with a 1080p 240Hz alternative), the motion clarity is easily good enough here so the spec difference isn't hugely influential for most uses.