I think once they've capped a queen cell there is no stopping them, I'm not sure i would have knocked the capped cell down without finding the queen 1st.
You're right, but I was just holding them back from swarming for a week by knocking all the cells down, and I graft my own queens so even if the queen has already swarmed I would not use the capped cell, I would put one of my own grafted cells in in a weeks time. I could not find the queen and had 22 hives to go through that morning, so knocking the cells down if I can't find her is my best option.
@louiseibbotson588 You might well be right, I probably will make a small split with her next week (if she is still there). I'm just trying to keep them in the box whilst the main flow is on, but I know I'm pushing my luck a bit😀