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This last pictures is a female Tolmerus (Machimus) atricapillus (could also be T. micans but that species has never been recorded in the UK). In the Netherlands Tolmerus atricapillus is called the "Common robberfly", together with Dysmachus trigonus by far the most widespread asilid. In NL it is rarer on chalk grasslands in the south. Very numerous on sandy soils. Machimus rusticus, on the other hand is only found on chalk grasslands in NL.

I am pretty sure this is M rusticus but based on looks, location and shape of genitalia. In the UK there is a look alike, M arthriticus. This species has usually more red on tibia, more slender male genitalia and prefers a sandy soil. To be sure the underside of the front femora should be visible, if there is only hair it is rusticus, if there is a row of bristles too then M arthriticus.