I believe Geraldo was a "house brand" of the well-known company Selmer, meaning they imported accordions from various factories in Europe and had their name stamped on them. The cheaper models were made in Saxony and aren't very good, but the more expensive ones were made in Italy and were pretty decent. Yours was probably one of their most expensive models in the mid-late 1930s, as it's a full size Italian instrument with four voices (denoted by the 120-4, which, looking at other Geraldos, seems to be a model number based on the number of bass buttons and treble voices). In working order it should be fun to play and have a pretty mighty sound! The problem is getting it to that condition. Cosmetically it looks ok and I'm guessing the bellows are alright - all my 1930s Italian accordions have great bellows, apart from the one that's actively falling apart! The keyboard, however, is a right mess. You want to take off the treble grille, number each key with masking tape and a pencil, and carefully remove the key axle from one end of the keyboard. They will all spring off into the stratosphere, so be careful! When you've got them all off, you can start to have a look at what's causing them to look like the accordion has been punched in the face. If you post some pictures on here, there will always be some people who can help! Aside from the snaggle-toothed keyboard, I can see you want a new set of shoulder straps - get some cheap ones on eBay - and at least one replacement bellows pin - someone on here might be able to help with that, otherwise you can trim down a nail of the correct diameter (make sure you trim it from the pointy end so you have something to grab onto when removing it).
These accordions are very common and not worth much at all, and while it's true that you could've got something in better shape for £40, you've got this one now. If I were you, I'd use it to (carefully) practice repairs on, and essentially use it as a test instrument. If you can get it working, that's great! If not, then you haven't destroyed anything of significant historical or monetary value. Good luck!