Another quick update. Ordered spare parts (screen and back cover which was no longer sitting firmly), replaced them on the phone and everything was as good as new. However, I discovered my GPS was not working. Checked with the *#*#66#*#* test, with the GPS test app and nothing was working. @Antoine suggested dismounting and re-mounting the entire phone to ensure alignment. I have proceeded three times with no success. I then just removed the screws and started mounting them using the star tightening method, which ensures alignement and everything was working fine again.
Just in case this is useful to someonelse as well. The screw order DOES matter (especially if your FP has had a tough life 
)