Before 1850, Acts of Parliament were written on parchment rolls in the neat script of the day. Earlier Acts were written in varying hands (some in what was called Chancery and some in what was known as the Secretary).

From parchment...

By James II's reign the more formal Parliamentary hand, Chancery, was winning. By the end of the 18th century, this script had superseded all others, and remained, although with a certain coarsening, the official hand for the writing of Acts of Parliament.

Many parchment rolls before 1850 contain visible amendments; knives were used to scrape away the script from the top surface of the rolls, before new text was added. This was due to the fact each Bill had to pass through various stages in each House on its way to becoming an Act.

Until 1850, a paper draft was brought into the House in which the Bill started; after the committee stage there, the Bill was subsequently inscribed on a parchment roll. This parchment was then passed to the other House and received any amendments there might be. But the Bill was never re-written, and the Royal Assent was therefore often given to a parchment containing numerous additions and deletions.

...to print

In 1850, manuscript acts written on parchment rolls were replaced by parchment codices (or booklets). Two copies of each Act were printed on vellum, one for preservation in the House of Lords and the other for transmission to the Public Record Office.

Since 1854, every Act was also passed by the assent of a Royal Commission, whereby the Sovereign also no longer gave the Royal Assent to Bills in person, but commissioned certain peers to act on their behalf.

This process, however, proved to be extremely inconvenient, and when printing was adopted in 1850, a final version was printed for endorsement by the Clerk of the Parliaments.