I would reccommend the NZXT S340.
It has more than enough space for your GPU (364 mm) and it has a nice side window.
£50 isn't exactly the sweet spot for getting a case. Most high-quality cases are just above that much (like the S340) and anything under that price looks like its going to transform into a spaceship (you've probably seen the £20 cases that have the weird shapes and colors)
You can get the S340 for £56