This is probably not a native British mainland species.
There is only one British record (a male from Deal, East Kent found in August 1882). However, the species does occur in the Channel Islands (Jersey, Guernsey, Herm and Sark).
Overseas, T. obscuripennis tends to be a southern and eastern species in Europe. It is not uncommon in north-west Africa, the Canary Islands and Turkey eastwards to the Caucasus.