I can't comment specifically on engineering roles, but for jobs in high finance and consultancy, UCL is the better choice hands down, no shadow of a doubt.
It's directly targeted by all the top banks and consultancies (apart from MBB which loves Oxbridge, but UCL grads still go there, just in far fewer numbers, but even that's bloody impressive), as opposed to Birmingham which isn't really on anyone's radar.
If you want a year out in industry you can take it - just take a leave of absence between years 2 and 3 and apply - the difference is that UCL doesn't help you out with anything.
Not sure what rankings you're talking about; UCL as a whole is a top UK uni, and top 20 world uni (even ranked 4th in the world by QS this year).
Social-wise - well that depends entirely on the individual.
In employment I meant non finance jobs. For those, from what I gather, go to the most prestigious university and then do the best you can to stand out in a positive way.
We occasionally went to the SOAS library because it was open till quite late.
There are a lot of societies and there's always something going on so I doubt you'd miss out if you went to UCL.
I was happy at UCL but I didn't like living in London but that's just me. It's very expensive and some of my best friends lived miles away so I could hardly ever see them.
There's quite a few but most of them probably won't be of interest for you if you're studying at UCL (although it depends on your subject area). I used the British Library a lot when I was working on my dissertation. It doesn't belong to the University of London but it's within walking distance, which is great.
I've taken this from Wikipedia as I could only name about 5 of them:
The nine largest colleges of the university are University College London, Birkbeck, Goldsmiths, King's College London, the London Business School, Queen Mary, Royal Holloway, the School of Oriental and African Studies and London School of Economics and Political Science, the specialist colleges of the university are such as Heythrop College and St George's, University of London. Formerly a constituent college,Imperial College London left the University of London in 2007.
Do you mean what makes it a campus? Essentially being a campus uni means all its buildings are located around one piece of land, like how school buildings are all usually on one site. A city uni such as UCL has its buildings dotted all around public streets and there isn't one central area. In Birmingham there are actually two campuses, but most courses are on the Edgbaston campus.