runner beans

I would of said it is. They are quite likely to stretch in the greenhouse and as the weather is turning autumnal, less bugs and bees are likely to be around to pollinate the flowers (if any grow before the colder spell) especially if they are in the green house.
Normal kenyan and french beans can be planted as late as end of July, but bit late for runners as take about 7-10days to come up, another 2 weeks to get to a decent size and then 2/3 weeks of climbing before first flowers, so thats end of Sept/beginning of October.
However now ive put doubt in your mind, you could always try some, you never know may have a hot september!

Try sowing some in succession, from late April through to mid June next year to get a longer cropping period. and the do freeze well incase you get a glut!