Okay guys problem has been solved!
Bolted the starter back in today but left the small start wire off and turned the key, main fuse didn't pop and I could hear the starter relay click so it had to be the starter. I then (just to see what happens) decided to connect the small wire back to the starter and turn they key and the car started with no issue. The only thing I can think of was that when I removed the starter it did have a lot of oil on it (rear main is leaking) and where it bolts up/earths to. I degreased and wiped all the oil off the area before refitting the starter.
I am going to replace the starter anyway just to be safe.(there is also a crack where it bolts on, see photo)
and obviously get the rear main done asap.
Thanks to everyone for your help with fixing this issue, now I can finally enjoy driving my car again lol