Years ago I used to grow them every year and always froze them. I prepared them for cooking, blanched them for a few minutes, cooled them and then froze them in portion sizes in freezer bags. They were fine.
Agree with the other gardeners... here in the U.S. they're called green beans (or yellow as the color may dictate). Picked at peak of tenderness, blanch (kills the surface bacteria) quickly plunged into ice water. But... we get better preservation by assuring they are quite dry and we use our ever-present vacuum sealer... I'd suggest one for any home gardener... about $120 here... but well worth it.
Blanch them for one minute only and chill in iced water. They're not great when frozen but OK for family in depths of winter i.e. I wouldn't give them to guests! I think they actually freeze better than French beans.