I imagine a similar organisation would be created if this passed. It would probably be quite a good idea really, if we didn't mess it up in a typical British fashion.
In relation to the issue of firearms (you'd be better discussing this on www.PoliceCommunity.co.uk), what's the problem? It would negate the need for dedicated local cops patroling the terminals armed.
Probably because the armed police aren't dealing with immigration or border issues; I suspect that a move to deploy armed immigration officials would be matched with a "fine,police (you'd be better discussing this on www.PoliceCommunity.co.uk) your own bleedin' terminals then" from the local force, followed by UKBA striking a quick deal with BTP.