The Attorney General of England is the only one of the "several gentlemen of the law" who is not explicitly named. The reason for this omission is unclear, but with a little detective work, we can determine with fair certainty who the "Attorney-General of England" was.
We don't know exactly when DeLancey asked for the Attorney General's opinion on the matter. It could not have been before May 26, 1800, since that is when Jack is said (in the complaint of 1803) to have escaped from DeLancey. It could not have been after 1802, when the pamphlet was published. The anonymous compiler of the pamphlet says he heard of the case "about a year ago", that is, probably some time in 1801. The compiler further states that "all this happened at the last September Term of the Supreme Court" and that he has since found "that the hearing of the motion was delayed till the September Term in the present year". With the "present year" being 1802, when the pamphlet was published, and the "hearing" being scheduled for one year after the original trial, as the pamphlet states ("the motion was ordered to stand over for argument to the Term in September next"), this means that the original trial must have occurred around September, 1801. Therefore the opinion of the Attorney General must have been solicited between September 1801 and whenever the pamphlet was published in 1802, probably before the hearing scheduled for September, since the results are not mentioned.
There were two Attorney Generals in England between May of 1800 and September of 1802: Sir John Mitford, Attorney General from 1799 to 1801; and Sir Edward Law, Attorney General from 1801 to 1802. Mitford became Speaker of the House in February, 1801, and presumably gave up his post as Attorney General at that time or shortly after. By September, 1801, when the original trial probably occurred, Edward Law was the Attorney General of England.
Sir Edward Law (1750-1818), also Baron Ellenborough,
was the son of Edmund Law, who became bishop of
Carlisle. Though his father wanted him to join the
clergy, Edward chose to to study at the Charterhouse,
Peterhouse College, Cambridge, and at Trinity, and
on leaving the university was entered at Lincoln's
Inn to study law. He became a barrister in 1780,
soon gaining a high reputation as a lawyer. In 1787
he was appointed to defend Warren Hastings in a
famous impeachment trial before the House of Lords,
and his ability in court was widely recognized.
Law was appointed attorney general in 1801 and was
elected to the House of Commons. In 1802 he received
the post of chief justice of the king's bench, and
was created a peer, taking Ellenborough as his title.
He became an member of cabinet in 1806, while still
retaining his post as chief justice, which provoked
much controversy. As a judge he displayed great
knowledge of the law, particularly in the area of
mercantile law, but was harsh and overbearing with
a distinct bias against the accused. While presiding
at a blasphemy trial in 1817, Law instructed the
jury to bring in a verdict of guilty; it is said
that their refusal to do so hastened his death.
He died in 1818, shortly after resigning his judicial
office.
Biography of Spencer Perceval