There is no mechanism for capturing additional earnings. It is possible for Civil Servants to have other sources of income over and above their civil service salary, where those present no, or no perceived, conflict of interest.
However those arrangements are between the parties and do not involve the Home Office. Staff are required to report these arrangements to their manager and no central record is maintained.
Gifts and hospitality offered and received are recorded and reported internally. The Home Office publishes details of permanent secretaries’ external meetings and senior officials’ business expenses and hospitality on a quarterly basis.
The most recent publication of data can be found here:
In order to ascertain whether the gift or hospitality was offered to or received from a law firm, we would need to scrutinise every entry on the register individually and this would represent a disproportionate cost.