After fixing a front wheel puncture and refitting the inner tube and tyre I noticed that the tyre was slightly twisted on the wheel rim. I put the wheel back on the bike and spun it to make sure the actual wheel was ok and it's definitely the tyre that's twisted and not the wheel. I even took it off again, removed the tyre and inner tube and put it all back again making sure everything was ok and it looked ok until I pumped the tyre up again to see it was still twisted. Could the fact that I rode the bike after I got the puncture, a few hundred yards to reach a pedestrianised area have caused the tyre to distort somehow ?
It may be that the tire has become damaged, but if you rode on a flat tire I'd be more likely to suspect that the rim has been bent slightly.
Remove the tire from the rim and carefully check the rim -- sight tangentially to the rim edge and look for any spot where the rim flange moves in or out as the wheel rotates. If you find such a spot, bike shops generally have tools to remove small bends in the wheel flange.
Also, with the tire off, rotate the tire in your hands while observing the beads. If a metal bead is bent you may see the bead waver in or out. A bent bead can possibly be corrected, though there is risk of the bead breaking. A "bruised" tire, where the cord in the tire has weakened, should be discarded.
When mounting the tire, you generally should inflate once, deflate, then inflate partially again. With the tire about half inflated, inspect it on both sides to assure that the tire bead is uniformly seated behind the rim. If a spot is "off" you can generally work it one direction or the other with your hands.
Poor tire seating can occur if the tube has an oversized patch (or multiple patches in one place) such that the tube does not inflate uniformly. If you have such a tube, discard it, except in emergency situations. When repairing a tube use the smallest patch that can be reasonably be made to work, and beware of patches near each other or a patch too near the stem.
It sounds like either the bead of the tire or the ridge of the wheel that holds the bead was damaged and lets an area of the tire bulge or bubble out in one area. It took a bit of looking, but does it look anything like the pics 3/4 of the way down this thread?
Most likely is that there is a weakness in your inner tube. Take the inner tube off the wheel and inflate it gently. If there's an area that bugles (especially if it's in the same location where your wheel bulges), that's probably the issue. If so, replace the inner tube.
Something like this can happen as a result of a flat tire, or the repair of a flat. It could also be due to normal manufacturing variances that can take time to reveal themselves.
Also possible is that the tire tread is damaged. Check for signs of wear or weakness in your tire's side walls, both inside and out. Also make sure that the tire bead (which 'grips' the wheel rim to hold the tire in place) is not damaged or worn. If it is, replace it, especially if it still bulges with a new inner tube.