Japanese Knotweed

Hi,

We’re a young couple currently looking at buying a house, but on our second viewing the agent told us that there’s knotweed in the garden. It seems to have taken up some of the patio.

They have managed to maintain it (from what we can see anyway it was chopped down), but said it needs to be treated a few times a year.

It came in from the neighbors garden.

How much of an impact would this have on this property?