Six weeks later, Mr.Williams went to town, and in the House of Commons walked up to and recognised the scene of the various incidents in the murder.
So far The Times, in 1828.

But two forms of a version of 1832 exist, one in a note to Mr.Walpole's Life of Perceval (1874), "an attested statement, drawn up and signed by Mr.Williams in the presence of the Rev.Thomas Fisher and Mr.Charles Prideaux Brune".

Mr.Brune gave it to Mr.Walpole.

With only verbal differences this variant corresponds to another signed by Mr.Williams and given by him to his grandson, who gave it to Mr.Perceval's great-niece, by whom it was lent to the Society for Psychical Research.
These accounts differ toto coelo from that in The Times of 1828.

The dream is _not_ of May 11, but "about" May 2 or 3.