Clue: Meat-carrying lorry losing roof (straight up!) (8)
Answer: VERTICAL
Explanation: Meat-carrying lorry losing roof (straight up!) (8)
**VEAL** ("meat") *carrying* (a)RTIC ("lorry" *without its roof (ie top letter)*) 
*Slight issue with, as I think the "losing roof" would be more appropriate to a down clue.