That's a lot of work for an A Level. My final year project report was close to 20,000 words, although was supposed to only be 10,000.
Although unlike having to write a dissertation, where the document is your work, our project report was, as you could imagine, about the project we'd spent the past few months doing. So there's more work to it than would first appear. Hmm, I'm off on a tangent in the first paragraph. :|
More relevant to the OP would probably be the technical authoring module I did, where we had to write a 3000 word report on something (+15 minute presentation). Now admittedly we didn't have to critically analyse anything, so we could just collect a load of information and present it in our own manner, which makes things easier. I think the advice we were given stills stands though, and that is to pick something as specific as possible, so that you can focus on it, as when you really start to dig into it, you'll find tons of content. For example, I like cars, but didn't write about the development of cars, nor development of engines, but specifically
The History and Development of the V8 engine (and as usual, I
still bust the word count).
HTH