Like many large companies, the place where I work has three flag poles out side which they like to use for a bit of decoration. Usually they get this right and fly the Union Jack from the middle one and two company flags, one at each side. When they get distinguished overseas visitors they like to honour them by flying their countries flag—and I think they get this wrong—they replace the Union Jack with the visiting flag.
I like to think of it as if it were a ship. You fly your countries flag from the main mast. If a French admiral comes on board you fly the Tricolour from a place of honour—I think it is the foremast. You don’t take the Jack down otherwise you are saying it is now a French ship.
I think the correct procedure (at the office) is to leave the Jack where it is and fly the visitor’s flag at the pace of honour, the right hand pole when looking from the road. If you get two visiting countries then you forgo your corporateness and fly the second one from the left hand pole. More than that and you have a party so I think you revert to just the national and company flags so no one is offended.
The Department of Culture, Media and Sport seems to think differently. They say that the Union Jack should be a the left followed by other country flags in alphabetical order as required and then other flags until all the poles are used.