Friday last, I dropped the bike in a town-centre car park, no big drama, simply my own fault. She went over on the right and put a couple more scratches on the engine bars and busted the brake lever. 

I had a spare set of levers so it was only a five minute job the replace it. I was then left with the old one with a nice clean break so I thought I would try to fix it with "Superglue" (cyanoacrylate) which seems to stick just about everything metal, just by way of an experiment really.   

I made the usual repair using a fresh tube and there is no way that is going to stick, it seems OK, leave it an hour then a slight tap and off it drops. What is occuring here, is this some conspiracy to prevent repair? 

Could be wrong on this, but I have never had success with useing superglue on metal.  It seems to work better with pourus (sp?) materials.  JB weld, or 3m plastic emblem adhesive ( I use it on metal ) works real good tho.  And believe it or not sometimes nail glue.

I work at a costume / fashion jewelry store and that what we use to repair broken stuff. 

There are superglues for various applications. The Loctite cyanoacrylates wark really well in contact with metals. There are types that work well in narrow gaps, others that work well on porous materials.

Nail glue happens to be a cyanoacrylate that is formulated to hold well on nails

So, Cal, as to your original question: Your superglue probably is a type that does not like grainy metal surfaces. Using accelerator ("Kicker") might get it to bond, though.

I remember reading that someone bored a hole into each piece of the lever, put a rod in, and superglued the rod in  with great success... Try that?

Cyanoacrylate is not ideal for bonding metal subject to stresses, it needs moisture to set and as metal has no moisture content it can only draw from the atmosphere which doesnt provide enough for a satisfactory cure. My view is that the only thing superglue is good for sticking is skin!! Companies such as Devcon, Loctite and Belzona market industrial adhesives that will bond the lever effectively with a strength approaching that of the parent metal but would you really want to? Personally The thought of it failing again just when you need the brakes the most scares me too much and I just cant believe anyone would advocate or even suggest trying to `stitch` the broken halves together for the same reason      My guess is that if the MOT/Inspection guys see it they will just laugh and point at the door.

http://www.belzona.com/
http://www.loctite.co.uk/int_henkel/loctite_uk/index.cfm
http://www.itw-devcon.co.uk/

Just get a new one! it will save you time and money

Yeah,  I had no intention of relying on a repaired lever, i was just curious to see what could be done, I'll get a new spare next time i order any parts or visit the breakers, thanks for the input.

Cal?
I didnt doubt for a min that you would consider using a bodged lever but someone else might have.