First/Business has been on my BP's in recent years and that has been sufficient to use the priority queue.

To be honest, at around 7:30pm to 8:00pm when I am normally transferring my experience is that the queues are pretty short and quick anyway; you head up an escalator at either the SW or NW end of the check in hall, do a U turn and head back to the middle.

As far as direction from the T4 A/C to the TBIT Business lounge go, assuming you already have your BP, do the following (from memory):
.

• Head out of the A/C, down the stairs/elevator and out to the T4 concourse.
• Turn left and head along towards exit/baggage claim as signed going to right as you approach the end.
• Do not take the escalator down to baggage collection - keep to the left of the escalator and looking looking ahead and you will see a manned security exit.
• Head though and you will find yourself on a mezzanine above the check-in hall.
• Take the short escalator down, head out to the departures roadway and turn left.
• Follow the footpath around as it around the right from T4 to TBIT and enter the check-in hall.
• Enter and then head along all the way to the back left - this is the SW corner.
• Go up an escalator and at the top do that U turn around to your right and ahead you will see security.
• Go through as normal - after security follow the walkway out to the departures concourse.
• When you come out to the large main area you should see some elevators to your right.
• Take these up to the *O lounge (go to the right after you exit the elevator).