Here is a site with more details on Sundays running order and that

I was pleased to see that there's a good non-sectariuan touch to the day - it starts with Mass in the Catholic Catherdral, where the parade starts and ends with Evensong in the Protestant church of St Martin's in the Field, off Trafalgar Square, wherte the free concert is taking place.

And there's an open stage as well as all the famus people on the main one. That's where the good music will be.