Alright, well you're going to want to replace that case and PSU at the same time, but they should be fine for now. I'm a little more worried about the case than the PSU since it's going to be tough to squeeze a decent GPU in to the case, but the PSU shouldn't have a problem running a half decent modern GPU.
You could get a new, decent quality(budget) case and PSU, as well as a new GPU, but you're limited to an entry level GPU;
PCPartPicker part list
/ Price breakdown by merchant
Video Card: Palit GeForce GTX 1050 2GB StormX Video Card
(£103.14 @ Aria PC)
Case: BitFenix Nova ATX Mid Tower Case
(£28.86 @ Aria PC)
Power Supply: XFX XT 400W 80+ Bronze Certified ATX Power Supply
(£39.89 @ CCL Computers)
This is still going to be a big upgrade over your current GPU though.
Otherwise, your budget allows for an RX 470, or even a 480;