In what circumstances will a declaration be admissible?

In The Queen v. Birmingham Overseers, supra, the proceedings were to remove a pauper from the parish. The pauper could not be removed if her husband's father (since deceased) had occupied a tenement in the parish at an annual rent of not more than £20. In proof of this fact she tendered a declaration by the father that he had occupied the tenement as a tenant - matter adverse to his interests - at an annual rent of £20 which was taken to be favourable to his interests. The declaration was admitted in evidence. Cockburn, C.J. said in part at p. 899: "Now, it has been held, over and over again, in the analogous case of declarations against pecuniary interest, that the declaration of the deceased person may be received not only to prove so much contained in it as is adverse to his pecuniary interest, but to prove collateral facts stated in it; at all events, so far as relates to facts which are not foreign to the declaration, and may be taken to have formed a substantial part of it." And again at p. 900: "According to the argument of the respondent's counsel, all that was admissible was the fact of his being a tenant; but that, when he went on and said, 'As tenant to A. B;' he stated more than was admissible. That circumstance is just as much a collateral fact as the amount of rent in this case. So far, therefore, as authority goes, it is in favour of the appellants. But independently of that, I should be prepared to say, that as soon as it is established, which it now is, on the authority of Higham v. Ridgway (10 East, 109) and the other cases, that you may receive the declaration of a deceased person, as shewing, not only something adverse to his interest, but all incidental facts contained in that declaration, so far as they are not foreign to it, it follows as a consequence that those collateral facts may be proved by the declaration; and that principle applies to the case before us."