UPDATE, April 3: Like many of you, we originally suspected this might be someone playing an April Fools' Day joke, but that doesn't appear to be the case. After doing some digging, and as we've reported on our Tours page, we believe the event was a late 50th birthday party for Apple design chief (and Friend Of Bono) Jony Ive. "Spike," the original source of information on Twitter and Instagram, is Richard "Spike" Holifield, who played bass on Sinead O'Connor's album, The Lion And The Cobra. He's now deleted all of his posts and photos from the event, but you can still see them on Storify. We'll leave our original story intact below, but the links to individual tweets won't work, nor will the embedded Instagram photo show up.
UPDATE, April 4: Dave Swift, bassist for Jools Holland, has further confirmed this secret/private gig with a post on Instagram that shows Holland rehearsing before the show with Bono, The Edge and others. Swift says he played bass for Bob Geldof, Marc Almond, Lily Allen and Bono, and that U2 performed after that:
"U2 were on after us, so I managed to have a chat with bassist Adam Clayton. He was due to borrow one of my vintage Ibanez Musician basses (he used these himself back in the 80's) but I believe he ended up using a Fender supplied by the venue."
That matches and confirms our earlier reports about Adam using a loaned bass (see below).
U2 played a private gig Saturday night in Oxfordshire, northwest of London. Little details are known other than what's been posted on Instagram and Twitter by "Spike," whose Twitter bio says he played bass with Sinead O'Connor and whose Instagram bio describes him as a musician and sound engineer.
Spike tweeted Saturday evening that he'd just been asked to loan a bass to Adam Clayton for the private performance:
"Just lent my #fenderjazz to some #bassplayer called #AdamClayton he plays in some band called @U2 it's a gig at a secret location."
That was followed up with several more tweets explaining how he delivered his bass to Dallas Schoo and got a £100 tip from Adam. In another tweet, Spike says he received a text message from Dallas S. telling him that the bass had been used on "I Will Follow," "Angel Of Harlem," "Desire" and "One." And on Instagram, Spike posted a photo that shows Adam playing his bass while Bono sings.
Needless to say, we've no idea what the story is behind this gig. When asked by a fan for a more specific location, Spike would only say it happened in Oxfordshire. I've collected all of the relevant tweets about it on Storify.