The solution

The event was The Marionettes Chorale Christmas show at Queen's Hall, a popular annual event, which I went to on Sunday December 6th, with pocket-size sketchbook.

The audience was in darkness while the performers on stage were well lit.

The pianist: Justin Salloum; the pannist: Johann Chuckaree. They played a lovely piece together, would it be called a duet? -- and they looked at each other often, nodding or making signs, and I thought it was a really nice and touching performance, the highlight of the show.

A Google search on "Christmas concert Trinidad" (without the quotes) brought up this link on the second page. Of the three concerts mentioned the only one with a pianist and a pannist was the Marionettes. Since I knew what I was looking for, you could cry foul!

Then I tried a search on "Christmas concert Trinidad pianist pannist" and got nothing.

Then tried again with "Christmas concert Trinidad pianist" and the Newsday link above came up first in the list!

A review of the concert

An old video of the Marionettes Chorale

Thanks to Duncan, Mark, Bri and Finchley land girl for taking part, and have a great Christmas everyone!