The "Potter" Wasp, also called "Mason" Wasp - both after the mud "pot" built for the nest egg, Ancistrocerus is difficult to identify to species level without microscopic or DNA analysis.
From the Latin name, one would expect Ancistrocerus trifasciatus to have three yellow bands or stripes, but its seems that is not always the case.
Moreover other Ancistrocerus species in the UK, A. parietum, gazella, nigricornis, campestris, quadratus and others, can also have three stripes. Males and females also differ in appearance.
This wasp has three bands on the lower abdomen, one cut away on the upper abdomen and a black face and thorax with negligible yellow markings.
This wasp also has three bands on the lower abdomen and one cut away on the upper abdomen, but has some yellow spots on the thorax and . . .
This wasp has four bands on the lower abdomen, one cut away on the upper abdomen, significant yellow markings on the front and back thorax and some yellow markings on its black face.
This wasp has a small notch cut out of the differently-shaped band on the upper abdomen (Symmorphus) genus, only two bands on the lower abdomen (S. bifasciatus), a few yellow dots on the thorax and a black face. Symmorphus crassicornis and Odynerus reniformis (not shown) have a small notch cut out on the upper band but have four lower bands.
This wasp has four bands on the lower abdomen, two reverse cut away on the upper and central abdomen, a large yellow blob with other markings on the thorax and totally different antennae to the shorter, hooked antennae (which gives the genus name) of the others above -- is not
Symmorphus genus and looks like an Ichneumon Wasp
imitating a Potter?