O - Opel
P - Porsche, Proton, Perodua, Pagani, Peugeot
Q - Quattro GmbH (does that count?)
R - Renault, Reliant, Rolls Royce
S - Skoda, Seat, Saturn, Subaru, Spyker, Ssangyong
T - TVR, Talbot, Toyota, Triumph
U - Ultima, Unique Motor Company (Noel Edmonds QPOD)
V - Volkswagen, Vauxhall
W - Wiesmann
X -
Y - Yugo
Z -
I thought that was a hint Celeste, it's getting very old, very fast unlike some of those cars