I was at the spring fair at RHS Hyde Hall yesterday and a lady at one of the stands said that once an Allium has a stem established with pre opened flower attached then you can cut back the leaves.
She stated that the leaves have by this time done their job of feeding the plant and that they can be removed. That said I have seen varying opinions elsewhere on the net.
All my Chritsophiis and Globesmasters have long stems with flower heads on (all un-opened) and all the leaves are now getting crazy long. I'm wondering whether to now cut back to half their length to make them look a bit more presentable?