Yes, the fold out prong (which is the upper of the three prongs in the triangular shape) is the "Earth" or ground prong. It is not a problem, as many plugs in the UK have only 2 prongs with an adapter. This is how many adaptors function.

I am Uk based and have lots of 2 prong items like this in the house. When you get to see the hotel bathroom in your UK hotel, you will see that there is normally only a 2 prong socket there which is used for shavers and toothbrushes etc.