Bumblebees are descending on the Broad Beans. The smaller bees are able to crawl right into the flowers. As seen above larger bees start with the frontal approach. If that doesn't work they move to the side and the back. They are able to pierce the tube of the flower with their long tongues and suck out the nectar.

 The white flowered beans are the stalwart Victorian variety Bunyard's Exhibtion [see entry dated 5th. April 2020]. Growing among them are Crimson Flowered Broad Beans, another heritage variety that owes its survival to a lady called Rhoda Cutbush [see entry dated 5th. February 2019 ]. The bigger bumblebees have the same problem with these (and the same solution).
 The term for it is "nectar robbing". The nectar is the lure for bees to pollinate the flower by entering it thereby transferring pollen from one flower to another as they forage. That doesn't happen if they bypass the pollen in the flower by nectar robbing.
 Certainly sufficient pollination does take place because both varieties are good croppers. I have found in previous years that there is also a cross pollination between the white and the crimson resulting in a bean that grows into a hybrid form with creamy pink flowers.