thats not a halfords e-stay
might be al carter , pacific , lew-ways and others
btw stx (even rc ) is not desirable yet(think 97 rock hoppers )
it will build a good hack bike and actually may suprise you how nice it is
if not and its a 19" frame give me a call
by the way this is a shit tip halfords e-stay
Carerra had a lower end estay with a different frame to the quattro which is a good bike (think that is the name) I believe it was the Kraken and it is very similar to the one in the first picture.
I actually don't think that's a horrible frame - throw a nice paint job on it and it will make a good hack. The curved, braced stays are actually very reminiscent of some Braves I've seen - like Nate's for instance:
I seem to remember those Ballistic forks being quite a pricey piece of kit once upon a time too.