Propodeum with a long median carina (ridge) dorsally; females are distinguished by a short ovipositor (sheaths are usually no longer than the hind basitarsus), making them distinct from other Braconidae; forewing with two (plus apical third) submarginal cells, second submarginal cell often longer than high. Cyclostome mouth, a circular opening formed by a dorso-ventrally short clypeus and a concave labrum, bordered below by the mandibles. The first three abdominal segments are heavily sculptured, often with longitudinal ridges.

There are thousands of species worldwide with about 40 UK species identified so far. Very difficult to identify  beyond species group:

Aleiodes apicalis group: Recognised by having the APICAL HALF OF THE HIND WING MARGINAL CELL DISTINCTLY GRADUALLY WIDENED (measuring at least 1.6x its width near the hamuli). If the marginal cell is parallel-sided, they display robust tarsal claws with a coarse, often blackish pecten. They also possess a wide, distinct, SMOOTH TRIANGULAR AREA MEDIO-BASALLY ON THE SECOND METASOMAL TERGITE, and an occipital carina that is usually reduced ventrally (failing to reach the hypostomal carina).
Aleiodes circumscriptus and Aleiodes bicolor groups: APICAL HALF OF THE HIND WING MARGINAL CELL IN THESE GROUPS IS PARALLEL-SIDED OR ONLY WEAKLY WIDENED (less than 1.8x its width near the hamuli). The second tergite lacks a distinct triangular area medio-basally. The occipital carina is complete ventrally (reaching the hypostomal carina), and the mesopleuron is usually extensively coriaceous or finely granulate.
Aleiodes gastritor complex: These species are incredibly similar and difficult to separate, but they are highly differentiated by their biology and strict host-plant or host-species specialisation. 

Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

The females deposits eggs in caterpillars of various species. The eggs hatch and the wasp larva feeds on the caterpillar leaving a hardened skin, or mummy. The wasp pupates within the mummy and eventually the adult breaks out, leaving a small hole in the husk of the caterpillar.

Common and widespread. 

Under recorded due to identification difficulty.