Mr.Pitt did not say that the Bank of England need not pay its notes in specie; he 'restricted' them from doing so; he said that they must not.
In consequence, from 1797 to 1844 (when a new era begins), there never was a proper caution on the part of the Bank directors.

At heart they considered that the Bank of England had a kind of charmed life, and that it was above the ordinary banking anxiety to pay its way.

And this feeling was very natural.

A bank of issue, which need not pay its notes in cash, has a charmed life; it can lend what it wishes, and issue what it likes, with no fear of harm to itself, and with no substantial check but its own inclination.

For nearly a quarter of a century, the Bank of England was such a bank, for all that time it could not be in any danger.