From the 12th century, Westminster gradually became the administrative centre of the kingdom. Under the Norman kings, the seat of government was wherever the monarch happened to be, with his clerks, parchment and sealing wax.
Treasury at Winchester
The only fixed department was the treasury at Winchester. However, as the institutions of government developed under the Angevin kings, it became increasingly inconvenient for them to move, and it was to be at Westminster rather than Winchester that they settled.
The most important institution was the government finance office known as the Exchequer, which originated under Henry I. By the reign of Henry II, the biennial sessions of its court were held at Westminster (although it still spent occasional periods at York or elsewhere until 1339).
Settled at Westminster
As it became increasingly inconvenient and dangerous to transfer large sums of money between cities, the main treasury eventually settled at Westminster by the reign of King John.
By 1244, the Exchequer was housed in a building adjoining the Hall (reached by a staircase in the north-west corner), which it continued to occupy until the 19th century.
By 1310, the Hall had also become the base for the Chancery. The Chancery was the chief secretariat of the Crown and was involved in every aspect of the administration; only later did it become a court of law.
The royal seat in the Hall was occupied by the Lord Chancellors from the mid-14th century onwards, who were said to have used the great marble table of Henry III, presumably for more formal activities like affixing the great seal.