This new channel is essentially a short cut, it turns out, and a bit of packaging to give a more exclusive feel. The new entrance is, as pointed out by
abitwild, by the Boots in North Security, to the left of the current entrance. You will need to know it's there since it's a bit buried. This is what you see as you enter off HEX or the Tube:
So normal North security is on the right of the photo past the Christmas Tree. The new entrance you can just make out next to Boots, under the giant TV. Here it is closer in:
There is an illuminated black and white sign, currently reversed, next to the yellow one for the toilets. If you go through this, it brings you straight to existing security lanes 1 and 2, the two closest to North Galleries Club. It is not in service yet, they are testing it, but hope to have it working in the next couple of weeks or so, in time for the Christmas rush. I doubt it will be a full time service, HAL are paying for this, not BA, and after 17 hrs or so it's hardly needed.
Having said that, overall, with some exceptions, security at T5 is a lot better than it was, thanks in part to the multi user tray loading points. They have some downsides, but on the whole it's now rare for security to take more than 5 minutes from landside (Flight Connections remains rather different).