On 7 June 1753, King George II gave his Royal Assent to the Act of Parliament which established the British Museum.
The British Museum Act 1753 also added two other libraries to the Sloane collection, namely the Cottonian Library, assembled by Sir Robert Cotton, dating back to Elizabethan times, and the Harleian Library, the collection of the Earls of Oxford.
They were joined in 1757 by the "Old Royal Library", now the Royal manuscripts, assembled by various British monarchs.
Together these four "foundation collections" included many of the most treasured books now in the British Library including the Lindisfarne Gospels and the sole surviving manuscript of Beowulf.

The British Museum was the first of a new kind of museum – national, belonging to neither church nor king, freely open to the public and aiming to collect everything.
Sloane's collection, while including a vast miscellany of objects, tended to reflect his scientific interests.
The addition of the Cotton and Harley manuscripts introduced a literary and antiquarian element, and meant that the British Museum now became both National Museum and library.
On 7 June 1753, King George II gave his Royal Assent to the Act of Parliament which established the British Museum. The British Museum Act 1753 also added two other libraries to the Sloane collection, namely the Cottonian Library, assembled by Sir Robert Cotton, dating back to Elizabethan times, and the Harleian Library, the collection of the Earls of Oxford. They were joined in 1757 by the "Old Royal Library", now the Royal manuscripts, assembled by various British monarchs. Together these four "foundation collections" included many of the most treasured books now in the British Library including the Lindisfarne Gospels and the sole surviving manuscript of Beowulf.
The British Museum was the first of a new kind of museum – national, belonging to neither church nor king, freely open to the public and aiming to collect everything. Sloane's collection, while including a vast miscellany of objects, tended to reflect his scientific interests. The addition of the Cotton and Harley manuscripts introduced a literary and antiquarian element, and meant that the British Museum now became both National Museum and library.
British Museum