Trim the runner beans: That is, pull off the strings and cut away the ends. Cut into bite-sized pieces.
In a suitable pot, boil plenty of salted water with a pinch of baking soda. Add the runner beans and cook for a few minutes until al dente. Strain and drain.
In a frying pan or saucepan, slowly cream butter. Dust flour over the top and toast briefly. Pour in enough hot soup to make a plump sauce while stirring vigorously.
Stir cream until smooth, add and also boil vigorously. Add the green beans again and season with salt, pepper and a squeeze of lemon juice. If the sauce has become too thick, add hot soup again and reduce briefly.
Arrange the creamed green beans in bowls and serve.