If its the same as mountain bikes (and mine was several thousand so its not your halfords jobby) then as martin says locking means nothing really.
Old style cantilever brakes can lock a wheel, but they are useless at slowing you down. You dont have enough control over them, and they overheat so quickly.
V brakes or magura hydralic rim brakes are better with more feel but still not exactly wild performance you can still lock at will.
Disc brakes are soo much better, its odd you can slow down faster on wet slippery mud and roots with a more powerful brakes than less powerful even though you cant use anything like the brakes potential. Hope 6 pot ventilated disc brakes are supposed to be the nuts, yes for a mountain bike! I want some!
http://www.chainreactioncycles.com/K...?ModelID=15211 these are drilled, but you can buy a drilled and ventilated disc.
The moral of the story is you can never have enough braking power
I fitted 4 pots from the R33 to my bluebird
and the S12 I just bought has the Z32 option fitted.