Most of the beetles here are from (unless otherwise stated) the group Cantharidae, known as the Soldier beetles. I've listed a few of the more common ones and a brief pictorial guide (with the aid of Cantharid queen Steph Skipp) to the often less-covered smaller species.
She would love it if you can send her any records via iRecord
There are many similar species and for the larger, brightly coloured species there are some excellent free guides already available.
If you like pictures try Mark Gurneys picture guide
If you like something a bit less colourful then Kieth Alexander & Martin Harveys field guide is HERE
For a key to all of the UK's species, there's also The Fitton Key
A very common species found throughout Britain in a range of habitats
sandy tan colour
Pronotum tan with dark 'Phallus' shaped marking
Shiny tan elytra completely covering wings covered in short hairs
Often occur in large numbers towards the end of the summer, known as 'blood sucker' or 'bonking beetles'.
Despite frequently being seen 'bonking' they have never been documented sucking blood and instead feed on pollen and smaller insects.
8- 10 mm
sandy tanelytra with black tips
red and black legs
Probably the most frequently encountered large species of soldier beetle in the UK
9.0 - 13.0 mm
Black wing cases
Black legs with red (femora) bases
Red pronotum with central heart-shaped dark mark
Small (under 5mm) black and yellow soldier beetles, often beaten from deciduous trees but occasionally turn up in moth traps.
They usually have black elytra with distinctive yellow tips They can be a bit of a pain to separate, but if you can separate the 2 Genera, you are already halfway there.
It is possible to split the 4 Malthinus species fairly simply (see below guide) however Malthodes are another kettle of fish and may require genitalia dissection.
For a key to all of the UK s soldier beetles, including genitalia diagrams
Splitting the Two
More boggle 'eyed'
roughly triangular head
mandibles with a tooth
Bell shaped pronotum
Head and/or pronotum more course with rough punctures
Less boggle-eyed in comparison (although some males do buck this trend)
mandibles without a tooth
A more square-shaped pronotum
Head and/or pronotum smooth, at most finely punctured
Malthinus- 4 species
Cantharid whizz, Steph Skipp showed me the easiest way, by far, to split the 4 British species was through pronotum patterns.
Be aware that often these markings can merge (in the case M. flaveolus particularly) and can be pretty variable, but its a great way to begin to split them, when used in conjunction with other ID characteristics
Pronotum patterns in UK Malthinus species
Punctures in rows
Pronotum with Black' hourglass marking
Scutellum with at least apex yellow
Pronotum with 2 lines, may merge to form a 'V' shape
Pronotum with thick vertical band with parallel sides
Scutellum entirely 'dingy brown' (fuscous)
Elytra have a horizontal(transverse) white line across it
Entirely black pronotum
Malthodes- 12 species
Of the 12 Uk species, I feel only one ID easilly recognisable in the field IF it is a typical example.
Personally I would recommend keying any other suspect Malthodes out properly.
Be aware there are completely dark forms that do occur and that they can be incredibly variable.
ID Features (of a typical specimen)
Pronotum with a lateral border when viewed dorsally (left)
Pronotum with all 4 corners paler, often forming a 'blurred' cross shape
Male with bulbous eyes and abnormally long antennae
Male (Left) & Female (Right) Malthodes marginalis)
The odd ones out
These beetles are not soldier beetles, (Cantharidae) and simply superfiscially resemble them, for ease of identification I have put them here.
approx 5.5-6.0 mm
metallic green body and legs
2 pink, well defined spots on elytra ends
Transverse pronotum (Wider than long)
Second antennomere strongly serrate
Only likely to be confused with the smaller Cordylepherus viridis which has smaller spots on the elytral ends, is overall smaller (4.0-5.5mm), quadrate pronotum (as long as wide) and with a less serrated second antennomere.
The Malachite beetle, incredibly common throughout the spring and summer months
image via: Wikicommons