The Inland Revenue.

Rabbi Rabinovitz answers his phone.
"Hello?"
"Hello, is this Rabbi Rabinovitz?"
"It is."
"This is the Inland Revenue. Can you help us?"
"I'll try."
"Do you know Sam Cohen?"
"I do."
"Is he a member of your congregation?"
"He is."
"Did he donate £10,000 to the synagogue rebuilding fund last year?"
"He will!"