He had also a private chapel of his own, as we read in an advertisement of his, April, 1750. "Several persons belonging to Churches and Chapels, together with many others, supposing the Marriages at May Fair New Chapel to be detrimental to their interest, have made it their Business to rave and clamour, but in such a Manner, as not to deserve to Answer, because every Thing they have said tends to expose their own Ignorance and Malice, in the Opinion of People of good Sense and Understanding. We are informed, that Mrs. Keith's Corpse was removed from her Husband's House in May Fair, the Middle of October last, to an Apothecary's in South Audley Street, where she lies in a Room hung with Mourning, and is to continue there till Mr. Keith can attend her Funeral! The way to Mr. Keith's Chapel is thro' Piccadilly, by the End of St. James's Street and down Clarges Street, and turn on the Left Hand. The Marriages (together with a Licence on a Five Shilling Stamp, and Certificate) are carried on as usual, any time till Four in the Afternoon, by another regular Clergyman, at Mr. Keith's little Chapel in May Fair, near Hyde Park Corner, opposite the great Chapel, and within ten Yards of it. There is a Porch at the Door like a Country Church Porch."
His wife died in 1749 whilst he was in the Fleet prison, which accounts for his inability to attend her funeral. Why he was imprisoned is as follows. By advertising, and other means, his Marriages at Mayfair were very popular, and interfered greatly with the Vested Interests of the neighbouring clergy, one of whom, Dr. Trebeck, rector of St. George's, Hanover Square, brought a lawsuit against him, in the Ecclesiastical Court. He defended himself, but unsuccessfully, for a sentence of excommunication was promulgated against him on Oct. 27, 1742.
Two could play at that game, so Keith excommunicated, at his Chapel in Mayfair, his bishop, the judge who condemned him, and the prosecutor, Dr. Trebeck, but none of them seem to have been any the worse for the operation. Such, however, was not the case with Keith, for, on Jan. 24, 1743, a decree was issued for his apprehension. This did not take effect till April, 1743, when he was committed to the Fleet; the marriages at Mayfair being continued, as we have seen, by Symson and Denevan.