So I went home and got the old tank from the attic earlier. Its at least 20 years old, was my grandfather's. I don't really remember what was in it, definitely Neon Tetras. There were two identical ones, the other was donated to a local school.
I then used it for about 5 years as a gerbil tank before it went back in the attic for 10+ years.
Anyway I couldn't find anything else so all I have is a glass box. Spent the last while cleaning it out.
Its 60 x 30.5 x 38 cm or about 60-65 litres if leaving some space at the top.
Now just need to figure out what I want to put in it and how much it'll all cost for the bits and pieces (and fish)