"Charters of gift" is a historical Scottish term for patents. From 1765-1875 these were recorded in the “Great Seal Registers”. More help on finding older Scottish patents is available from the National Records of Scotland.
Most British patents from 1890 onwards are available in Espacenet, although coverage is incomplete until 1930.
English and Welsh patents were recorded in the "patent rolls" until 1852/3. (The patent rolls were the official record, so didn't just include patents.) In 1852 all patents were copied out of patent rolls and given numbers: GB1 (1617) – GB14359 (1852). Epacenet has added a year to the older patents e.g. GB176900913.
The British Library and The National Archives can help with tracing older English and Welsh patents.
A useful summary of historical and current patent systems in Ireland can be found on the Irish Patents Office website.
Prior to 1853, Ireland had its own patent system. These records are believed to have been lost in the 1922 fire at the Irish Public Records Office. However, a project is currently underway to trace and digitise any copies of pre-1922 Irish public records.
The British Library may be able to assist with finding post-1853 Irish patents.