In the course of the year 1818 a somewhat singular question as to the position of the Regent was raised by a claim advanced by Colonel Berkeley to produce his Royal Highness as a witness in a court of law.  The Prince consulted the Prime-minister, and the Prime-minister referred it to the Attorney and Solicitor General, not concealing his own impression that it could not be consistent with his constitutional position and prerogative for the King to appear as a witness to be subjected to examination and cross-examination.[177] They, in their statement of opinion, assumed it to be an undeniable principle of the constitution that the sovereign, “by reason of his royal character, could not give testimony.”  And therefore they had no doubt that the Regent, exercising his authority, was equally prevented from so doing.  Colonel Berkeley’s counsel had urged that, even if he could not appear in open court and be sworn, he had the privilege of communicating his evidence in a peculiar mode, by certificate under the Sign Manual or Great Seal.  But the Attorney and Solicitor General professed that they could not discover whence this last privilege was derived; they urged, as an insurmountable objection to such a contrivance, that “all instruments under the Sign Manual or Great Seal must, in point of form, be in the name of and on behalf of the King, which would manifestly be incongruous when the evidence certified was not that of the King, but of the Regent himself.”  And they quoted a case in which Lord Chief-justice Willes had said “that the certificate of the King, under his Sign Manual, of a fact (except in an old case in Chancery) had always been refused.”  As it had been urged also, on Colonel Berkeley’s behalf, that the Prince had formerly “joined in proving the will of the Duke of Brunswick,” his brother-in-law, they farther expressed an opinion that “he ought not to have done so, but should have left it to the other executors.”

On the point whether “the King himself could give evidence orally or in any other manner,” their opinion expressed very plainly the principle on which they maintained that he could not.  “That he was not compellable to do so; that he could not be sworn (there being no power capable of administering an oath to him in a court of justice).  That, whether his testimony be given viva voce or otherwise, no question in chief or on cross-examination could be proposed to him, was admitted by Colonel Berkeley’s counsel.  And that his testimony must be conclusive as to the facts stated by him, appeared necessarily to follow from the perfection ascribed by law to his royal character.  For such remarkable exceptions, therefore, to the case of all other witnesses they could not but think that strong and decisive authority ought to be produced; while the silence of text-writers on the subject, so far from being favorable to the notion that the King can give evidence, appeared to afford a directly contrary inference.”  And they summed up their opinion in a few words:  “that his Royal Highness the Prince Regent, while in the personal exercise of the royal authority, was in the situation of the King in this respect, and that the King could not by any mode give evidence as a witness in a civil suit.”