If taxed it's not abandoned, although one should check with the owner and police stolen vehicle records. Flat tyres do tend to imply the owner has either abandoned it or had it stolen though. The council should check.
Had some 'citizen' pretend my TR7 was abandoned once and the 'wonderful' council insulted me by shoving an abandoned notice on it's windscreen. Told them exactly what I thought of their malicious offensive action, and since they then decided to do it again I had to tell them again.