Hi Dunc, my strategy is a bit different to others. I break every swarm cell down when I find them. I like to allow a split to make emergency queen cells, it gives them more time to wait for the emerging queens & hopefully suppress those bees desire to swarm. If I find a strong hive with charged & well advanced queen cells, I take every frame of brood out to unite with weaker colonies, except for one, minus the queen cells. The frame with the youngest brood, I put that in the middle, just in case I have accidentally killed the queen & fill the rest of the brood box with frames of wax foundation. Then take a look in a weeks time. Normally the desire to swarm has passed.
Getting back to the emergency queen cells. If I have more than one frame containing queen cells in a split, I’ll often use that frame in later splits if I want that split to produce a queen a bit faster.