..continued. Remove the rad brackets off the wall. Complete tiling, drilling holes in tiles where the rad bracket holes are. Grout. Re-attach rad brackets. Re-aatch rad. Refill with water.
Be aware that you must be able to move the pipework attached to the rad as tiling will move it forward by 12mm or so. If you can't do that, you'll have to tile around the brackets.
Further to buildersmate's answer, if you cannot move the supply and return pipes you may be greater or lesser throw out from the wall. able to turn the brackets through 90 degrees. they are made asymetrical to to give the option of a greater or lesser throwout