This is a medium-large (2mm), surface active springtail that is reasonably distinctive, though may be confused with Lepidocyrtus, and which has turned up (through online macro-photography websites) in several locations in the south-eastern UK since 2000, but which has never been noted in UK Collembola literature nor does it feature in Steve Hopkin’s AIDGAP key nor his online distribution maps. There is a puzzle here as Steve undoubtedly saw this species - his photographs may be seen on Collembola.org. There must remain questions about the validity of identifying such small animals from macro-photographs alone (though the annulated 4th antennal segment is helpful), but in addition two specimens were collected from a pitfall trap in an apple orchard in 2008 by Michelle Fountain, and ID confirmed by Frans Janssens. Subsequently vortex sampling off plants in RHS Wisley found Heteromurus major to be one of the commoner Collembola, though with a surprising variety of apparent colour.
Separately this species has started turning up thinly but widely in Europe: Frans Jannsens has found them in Belgium, Jurgen Schultz found it in a saline meadow in Germany and Arne Fjellberg found it in a disused chalk quarry in Sweden. Given that this species only features in the (elderly, German) 1960 key by Gisin and has hardly been mentioned since, this appears to be another springtail whose range is on the increase.
Distinguishing this species from the common, widespread Heteromurus nitidus is easy, as H. nitidus is pale with 1 red-brown ocellus while H. major is brown, conspicuously scaly with 8 ocelli. Separation from Lepidocyrtus is based on the ratio of abdominal segments 3 and 4; in Lepidocyrtus there is a clear ‘saddle’ effect with abd. 4 at least twice as long as abd. 3, while in Heteromurus this ratio is somewhat <2. (Warning: if you measure from the animal's side view the ratio is very close to 1:1, leading to a dead end in the key). If you have an odd thing like an isotomid but very scaly, scales visible on ant1-2, and ant4 is annulated/corrugated/concertina-ed then you almost certainly have this species.
To see this 'saddle' effect, compare
with the clear and elongated abd4 on this Lepidocyrtus:
The AIDGAP key will take Heteromurus nitidus down to genus correctly, but only gives the option of the pale, 1-eyed H. nitidus.