Runty runner beans

Drawn leggy plants always take an age to perform, and sometimes just don't. But they still might with the right conditions.
You could try nipping the tops of a few and see if that improves matters. That will certainly be a quicker option than sowing afresh that will only catch the end of the season. Do both, and also leave a few as they are, and note what happens for future reference. We all learn from direct experience.
Are they planted in a favourable full sun location, as I would have thought they would have picked up by now having been planted out 4 weeks ago. Let alone the fabulous growing weather of the last 3 weeks ?

thanks both for your replies - yes, they're in a sunny spot and I'm also surprised that they haven't started to flourish. Gave them a really good watering yesterday but will do so again tonight and pinch a few of the tops out, too, as well as plant a few seeds as back-up. Don't think I'll be able to get any plants anywhere now.