What qualifies a taxon to be considered by the (1 Viewer)

I hope, this is the right place for this question:

what qualifies a taxon to be included in the list that is assesed by the British Birds Rarities Committee? Is it purely the number of birds seen in a year over a certain period? Or are there other factors that are taken into account?

Thank you

I think there are a number of factors involved, and these were outlined in some details by a serving member of the committee on another thread recently, I'll have a look and try to post a link. There appears to be some plasticity in the approach, so species status is reviewed and can be added back onto the list, a recent example is Kentish Plover, which has had loads of historical records and formerly qualified as a "scarce migrant" and was demoted, then became considerably rarer in the last decade, and was reassessed accordingly.
This link may be of interest, and I'm sure that others with more experience can help you understand further - I've limited experience with BB rarities sadly, the rare birds I've been lucky enough to find have mostly been demoted a year or two previously!

This is from the BBRC website:

4.1.1 Definition of a BBRC Rarity
The starting point for defining a national rarity is either 100 or fewer individuals in the most recent ten-year period, or ten or fewer individuals in at least seven of the last ten years. Any taxon that meets, or is close to, either of these criteria, will then be considered for inclusion as a BBRC rarity.

The Committee will also consider other factors such as population trends, distribution changes and identification issues.

4.1.2 Removal of a BBRC Rarity
All taxa currently assessed by BBRC will also be looked at, to check they remain rare. The starting point for removing a national rarity is either more than 100 individuals in the last ten years, or more than ten individuals in at least seven of the last ten years. Any taxon that meets, or is close to, either of these criteria, will then be considered for removal.

The Committee will also consider other factors such as population trends, distribution changes and identification issues.

Once a taxon has been dropped as a BBRC rarity it would not normally be reinstated, even if the criteria of Section 4.1.1 are met, until 10 years have passed.

https://www.bbrc.org.uk/about/constitution/4-bbrc-taxa

Thank you Daniel and Mark! That is the information, I was looking for.
I tried to find your link in birdforum, but there are so many results when searching for BBRC, so I would be glad, if you can find it, Daniel.

This is the thread I was thinking of, though there is not so much information that isn't included from the link that Mark and I shared, there is some explanation from Paul French.

Hope this helps!

Thank you Daniel!