Found settled on branch in a wood pile, sunny spot in urban garden.
No interactions present.
Clytus lama does look very similar to Clytus arietus, but C. lama is not on the British list. There is some information about C. lama at:
(you have to scroll a long way down the page to find it)
The above website tells me that C. lama has antennae which do not get darker or thicker towards their tips, whereas C. arietis antennae do, and on your photo we can see this darker area on the antennae. So I'm sure that yours is Clytus arietus, as anneriley suggests.
Entomologist and biological recorder
Lat/Lng: 50.9, -3.3
OS grid ref: ST1321