Charging iPad 3rd gen using cable and plug provided is VERY slow - like a trickle charge. If I had the wrong plug I could understand this but can anyone explain?

Are you using the iPad at the same time? If you are, it will charge quite slowly. The absolute best way to charge your iPad is to connect the wall charger to your iPad and when you hear the charging chirp, power your iPad down completely. It charges most effectively when it is completely off. Because the new iPad battery is twice the size of the previous battery, the charging cycle can range (depending on the level of the battery) up to 5 hours even with iPad completely powered off. I personally charge my iPad at night when I'm asleep and don't need my iPad.