Yes, you can generally use a cardboard (carton) box as checked luggage at UK airports, provided it meets the airline's specific size and weight requirements. Most airlines treat a box exactly like a suitcase, typically allowing a maximum weight of 23kg (50 lbs) for economy and total linear dimensions (Length + Width + Height) of about 158cm (62 inches). However, because cardboard is more susceptible to tearing or moisture damage, you must ensure the box is "heavy-duty" and securely taped with reinforced packing tape. Avoid using boxes with "hazardous" labels (like those from cleaning supplies) as security may reject them. Some airports or airlines might require you to have the box "shrink-wrapped" in plastic for a fee at the terminal to prevent it from bursting on conveyor belts. It is always wise to write your contact information directly on the cardboard with a permanent marker in case the paper luggage tag falls off. Note that some specific international destinations (like parts of South America) may have seasonal restrictions on checking boxes, so double-check your airline's destination-specific policy.