In any event, the one Android phone we had between us seemed like the best tool for figuring it out, even if the internet connection was as slow as treacle. We used Google Maps, with satelite view, slowly scanning the south of London for three very distinctive white wind turbines atop what looked like a distinctively-ovoid silhouette from above. Nothing.
We didn't spend that long looking, but the building was mysteriously hard to pinpoint. We enjoyed the wedding party, and celebrated into the still-warm darkness. South London faded into crypticness, and we made new friends and saw older ones. Usefully, I was introduced to the reviews editor for Vector, because London is a small place, really.
But we also went back to searching as soon as we were home again, C. to perusing the map, and me to rapid brainstorming. The puzzle was resolved by means of the search terms "south London skyscrapers". There, on the Wikipedia list of London's tallest buildings, at #15: Strata SE1. To be the tallest residential structure in the city once it's completed, theoretically this month. Distinctive white wind turbines installed in May 2010. Too recently for the last satelite photos on Google.
Google Maps are forever out of date a little out of date, just as all maps are.
Congratulations to coughingbear, hano, eulistes, margotmetroland, and drpete on their respective weddings yesterday!