Japanese knotweed

https://www.gransnet.com/uploads/talk/202604/medium-9kbln3-1000022589.jpg https://www.gransnet.com/uploads/talk/202604/medium-fncu7i-1000022586.jpg

I'm about to put my house on the market and have identified a crop of JKW at the far end of the garden ground
It's a wet area so probably extends beyond my garden, following the nearby riverside.
It's a good distance from my house and has been there for years and not bothered us.

I have had a quote for a survey of £500 and who knows what the actual cost of removal would be.

My friend tells me to attack it with systemic weedkiller and so deal with it myself.

Any advice welcome?
It's just coming out now, looking innocent and pretty among the wild garlic and goose grass .

I'm also told if you pretend you haven't got it and sell the property, the buyers could sue me for a hefty fine.

My home report last year didn't pick it up but I now have to have a new report.