Should be okay rootwise so close to the house, but make sure you plant at least a foot away from the house wall, preferably 18 inches to 2 feet, and train the stems back against the wall. It's a rambler, so September is the month to prune them anyway -by removing diseased, damaged and flowered wood, leaving intact any new, vigorous shoots. Transferring to the ground now is fine, but remember to keep it watered till end of October if we have any dry spells (oh how I wish...lol!)
And a word of advice - make sure you have already got in place a support system on the wall which will take a rose of this size - it gets 15 feet, and trying to add supports once its planted in the ground is no easy job.

Thank you very much for your exceedingly speedy reply! That's really helpful, and I 'm pleased that I can do it when my friend is here as I suspect it's going to be quite a struggle to get it out of the pot.

You can cut off all long stems if you want to make it easier - but you may lose the flowers next year if you do.

When you dig a hole for your rose, I would suggest that you place a polythene barrier below the foundations so that the rose doesn't have to compete with them for moisture.

Thank you both. I will get cracking next week!