Dusky Ladybird Scymnus rubromaculatus
This species was not included in Roy and Brown (2018), but has been established in the London area for a while now. It has only been found by a few coleopterists, several of whom work as professional ecologists.
In 2018 I found two all dark inconspicuous ladybirds in Euonymus shrubs, one in Waltham Abbey, Essex on 15th July and one in Upshire, Essex on 26th July.
Using my knowledge at the time, I identified both as Heath Ladybird. However, I became uneasy with this identification, as they were in a habitat associated with the adventive or recently established species. As they looked very like Red-flanked Ladybird, I wondered if these could ever be all dark.
I also wondered if they might be Dusky Ladybirds, but my knowledge of this species was confined to the two dots present in the NBN Atlas.
In August 2019 I obtained a copy of Mark Telfer's 2015 article in The Coleopterist, (see References in Introduction section), where he outlined how Dusky Ladybird is now widespread in the London area. He also commented on how Dusky Ladybird resembles an all dark Red-flanked Ladybird.
I have counted my two records as Dusky Ladybird for my own purposes, but they are not provable and I have not submitted them.
The following list of records is taken from Telfer (2015):
2000 20th July Stratford, London several swept from dry canal side vegetation Dan S. Hackett
2006 31st Aug Sheppey, E. Kent one male, three females On low hawthorn shrub, with ivy and bramble Norman Head
2010 Battersea Wharf, Surrey Jonty Denton
2013 24th May Gallion's Reach, S. Essex Jonty Denton
2013 7th Aug Silvertown Quays, Newham, S. Essex one male, two females found by tapping mugwort Mark Telfer
2013-2014 survey work on a green roof Greenwich, W.Kent produced a total of 13 males and eleven females, alongside 69 Red-flanked Ladybirds Mark Telfer
2014 Bampton Cemetery, Oxfordshire beaten from cypress tree Jonty Denton
Identification Length 1.8-2.3mm
This species is shaped like Red-flanked Ladybird, but the pattern overlaps with Heath and Schmidt's Ladybird.
Schmidt's can be ruled out as it has a groove along the centre line of the metasternum.
Dusky and Heath are both sexually dimorphic, males have a red face and front edge of the pronotum, whilst females (and possibly some males) have a black face and pronotum.
Both species lack a groove along the centre of the metasternum.
On typical males the orange red colour on the pronotum, (section behind the head), is more extensive than the similar species.
On many specimens the red covers most of the pronotum, with a small patch of black, either a triangle or semi-circle, at the rear.
This feature, combined with habitat clues, should make many males identifiable in the field, at least once it is generally accepted that this species is more common than records currently suggest.

Typical male markings
Females of Dusky Ladybird may not currently be identifiable using external features only as they are very similar to Heath Ladybird. My own records are based on habitat and instinct, they have not been verified.

Waltham Abbey, Essex

Waltham Abbey, Essex

Waltham Abbey, Essex

Upshire, Essex

Upshire, Essex
In August 2020 Mark Hows found a tickable (though unverified) individual at Purfleet, Essex. As with my records this was a female or possibly an all dark male form.
This one was beaten from Buddleja along the Thames riverbank walkway, in an urban setting.
The habitat and area are right for Dusky Ladybird but unlikely for Heath Ladybird. Also the shape is very similar to Red-flanked Ladybird which is a supporting feature for Dusky Ladybird.
.jpg)
Photo by Mark Hows
Purfleet, Essex
.jpg)
Photo by Mark Hows
Purfleet, Essex
.jpg)
Photo by Mark Hows
Purfleet, Essex
.jpg)
Photo by Mark Hows
Purfleet, Essex
Habitat
Both of my putative records were beaten from Euonymus shrubs, in two different gardens. Both of these two small shrubs also regularly produce Red-flanked and Epaulet Ladybird records. These are two common adventive or recently established species and are likely to overlap with Dusky Ladybird.
In contrast Heath Ladybird is a native species of semi-natural habitats including grassland and heathland.

Euonymus. Waltham Abbey, Essex

Euonymus. Upshire, Essex
The Purfleet individual was beaten from Buddleja in an urban setting.
The best plan for finding Dusky Ladybird would be to search low vegetation and shrubs on brown field sites in East London and the Thames Estuary area.