No, sorry, not Cylindromyia (they are a bit longer and thinner than this fly). This looks like Mintho rufiventris - rare fly in England but fairly common in Europe I think.
OK, I agree. Chris. It might be a Mintho rufiventris.
But Mintho rufiventris I saw, has much more bristles on the abdomen than this fly (You are right Cylindromyia has slender abdomen)