Airfix has produced a number of injected warship kits of the Cold War period. If the original kit came with decals, they probably have yellowed with age, or the decal sheet did not have the right hull numbers for the particular ship that you wished to build. You may have tried other decals but now there is no need to experiment, as Hawk Graphics has a decal sheet specifically for 1:600 scale modern Royal Navy warships. This sheet is numbered D6001 and consists of three sizes of black numbers on white outlines. The largest size can be used on all RN warships frigate size or larger. The next size is for the stern numbers of the larger ships and the smallest size is for the smaller combatants. Incidentally, Hawk Graphics also has Modern Royal Navy hull numbers in 1:700 scale.