On the subject of the identifiability of spinoletta v's littoralis, I sit on a local rarities committee in the Midlands, where the picture might superficially be clearer. One would think that in middle England, spinoletta (spin from now on)would be regular in spring, whilst petrosus/littoralis (pet/lit) would be less common, being supposedly a coastal bird.
This is not, however, the case. There are hundreds of records of "Rock pipit" in the last 30 years, averaging about 10-15 per annum. Spin however, has averaged 4-6 records, of 6-20 birds, in the last ten years. Given that all of the Rocks are most likely to be litts, this may suddenly throw into doubt some of the spin records.