I do not really know what I am talking about here, but am i right in saying there is a type of back brake that clips on to use, if you wanted to and the frame was not drilled for a back brake?
And if they do exist, what are they like and where does one get one? and do people think they alright?

You can get rear clamp-on (keirin) brakes. Dia-compe make some called BRS so maybe google that. They used to be easier to get than the front ones... I believe Brick Lane Bikes had some, also try www.benscycle.net (best bet, IMO). Freshtripe.co.uk get them in on occassion too, but very sporadically. I think you can get them from some BMX places too so you may want to try alansbmx.com.

Get dia-compes from billy's bmx shop based in the UK & good price.

www.billys.co.uk

Why do you want a clip on rather than a permanent fixture?

cavendish cycles usually stock them for £25. highly recommeded store so go down there and check them out. (call first to confirm they've got them instock)

website:http://cavendishcycles.wordpress.com/
contact them by: http://www.allinlondon.co.uk/directory/1284/2865.php

i've got one from them. reccomend taping up the frame to prevent the plates scratching off the paint.

My guess, because a drilled frame is less desirable and thous have lower resale value.. I'd not buy a drilled track frame..

i put one on my gf's bike. It was one of the diacomp ones from billys that someone mentioned up there^. It's fine but the stays on her frame were ali and a bit fatter so the bolt on it wasn't long enough. Also, depending on the position of the rear bridge you might not be able to get it on - without drilling the bridge. In the end i drilled the bridge and used the plate as well as i'm not sure if they spec a heavier duty bridge if they know a brake is going through it. Plus it wasn't exactly a museum piece i was building. They probably also didn't anticipate an idiot with a makita making the hole either...

End of the day it works but you might be in for a good bit of bodging. Ideally go to a shop and check it will work with your frame.

B.