Barclays does have its own system which is nothing to do with Currenex.
I used it years ago when I was trading for someone else and an ex colleague still does. I seem to recall he likes it very much although think it goes quite wide over figures.
Does anyone know what the commissions are for futures? I make an enquiry with BARX a few years ago but my net worth wasn't high enough at the time so the conversation didn't last very long.