Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
It's been awhile, but I seem to recall checking in downstairs but using the fast track security upstairs.
There will be a dedicated IB queue for Business / elites at the general IB check-in counters, so you aren't likely to be waiting long.