The British Open
This is a distinct competition within the British Open Series for Class 1. Its origins are historical.
Once upon a time, there was "The League", a series of three week-long contests, one of them overseas. Entry to the League was highly competitive, with only the most successful cross-country pilots allowed in. At the end of each year, pilots in lower than 35th place in the League were relegated and had to re-qualify to rejoin. In addition, the British Open was a separate, standalone competition for all comers.
The decline in numbers led to the League system being abandoned and replaced by the British Open Series, which incorporated the old British Open. Entry was opened to anyone with the appropriate pilot rating. Now, one round of the BOS is designated the British Open Series Open Competition for which the British Open Trophy is awarded.
The British Open will normally be held in Round 1 unless there are no scoring tasks in that Round.