And we cannot get it to grow at all.
Try a Systemic weedkiller like Glyphosate.

Thanks for your reply. We have tried spraying with two products containing glyphosate, Roundup and Weedol but perhaps we need more extensive spraying.

It does take a few sprays for some things to die. I have been spraying Japanese anemones for nearly 20 years and they still come back.
Best of luck.

Sorry to ask, but Invading your house? In what way? If its coming up through the floor, are you certain its Romneya?

A friend of mine had a similar problem - it came up between the skirting board and floor in his house.

It has managed to either pass through or under the stone outer wall of our house and has traveled under a damp proof membrane and is coming up behind the skirtings.

In one place it traveled up the wall up to ceiling height behind plasterboard.

I have added a couple of photos.

Surely this is a serious problem? Looking at your photos I would be worried and contact my insurance company for advice etc.

Unfortunately my buildings insurance covers events of a sudden nature but not those resulting from slow change (i.e. growth).

To those who answered the question -Pmscott has addad a photo in his Photos section - worth a look! Can quite understand his concern...

It is still worth ringing your insurance as they can recommend an expert and this service is often covered by them and is free even if they do not pay for anything else. What worries me is the value of your property! a survey may find it is unsellable unless it is irradicated and full repairs done.

Dear oh dear, that's horrifying (the photos). There is a product called Paradise; its used by groundsmen in rough or shingled areas where they don't want anything grow for six months. As I understand it, it kills anything that's growing currently, but its main purpose is to prevent germination of new plants,so I'm not 100% sure it'll do the job you want. You won't find it in any commercial garden supplies outlet,but an internet search should come up with a supplier; however, its expensive. I can't think of anything else that might tackle this,although I'm not sure how safe it would be to use indoors. Said to be more effective if mixed with glyphosate, but you'd need to check the information on that - there's stuff on the internet about it. If you use it on the ground where the plant grows outdoors, it might knock out what's growing inside, but I'm not sure about that either. The trouble is, if you use it on the soil outdoors, it will kill anything that's growing there, though that's probably a small price to pay given the problems.

I certainly think a persistent attempt should be made to dig it out on the outside. If you decide to use Paradise, check the regulations concerning it - the link below is to the Pro Green supplier and they have an advice line.

https://www.progreen.co.uk/paradise

Thank you Drc and Bamboo for more interesting suggestions.