Originally Posted by Pat+

United does a pretty terrible job at advertising and documenting the benefit.

No, you don't need to ask before departure - just walk in with your boarding pass. The clause about requesting access in advance applies to partner hotels and not lounges, and then again, typically you need to make the request when you land and not prior to departure.

You'll be fine - whether at LHR, or SFO, or FRA or ZRH just show up and you'll be admitted.

And a shameless plug, I just happened to write this post for LoungeReview.com which clarifies usage rules, precisely because united.com is so unhelpful: The Definitive Guide to United BusinessFirst and Global First Arrivals services

Enjoy the Arrivals lounge. It's one of United's best services.