How did I not know how easy it is to do your own royal icing and how much nicer/tastier it is than shop stuff.
I used 2 pasteurised egg whites as I'm a bit paranoid, 500g icing sugar, teaspoon glycerine and a bit of lemon juice. Mixed it all up and beat it hard. Then smeared it on and dd made it all peaky with a knife. It took no time at all and looks really fab.