Weeding and removing undesirable plants from your garden and property can be very time consuming and physically exhausting. The weed might also be destructive to the foundation of your property, like Japanese Knot-weed which will require specialised removal and certification so that you can sell your home in the future.
For this reason you will probably want to hire a local gardener or property maintenance company to remove these unwanted pests so that they don't take over your garden and property with what can be very costly consequences.
Weeding beds and lawns would normally be classed as a general service that a gardener would automatically do as part of regulary garden maintenance and the spraying of herbicide or weed killer.
Things get a bit more complicated with evasive and destructive Japanese Knot-weed which requires a specialist company to remove and certify the removal for future property sales. Companies like these require specialist equipment to remove the weed and to make sure that all traces of the weed have been removed. These companies will tend to quote for doing a job and tend to be more expensive than hiring a local gardener to weed your lawn.
Make sure you check references before hiring a Gardener or Gardening Service.
Japanese Knot-weed originates from Asia and was brought to the UK because of its good looks. Unfortunately it grows at a rapid rate (4 inches per day) in the UK away from its volcanic natural habitat where ash would restrict its growth. The plant also does not have any preditors and can swamp other plants within a couple of weeks.
The plant does not seed but can multiply from minuscule fragments of rhizomes which is bad news for properties that have been affected. Unfortunately the weed can, if left unchecked, damage your properties foundation and restrict or damage drainage and pipework.
To remove it you have a few options, but it can be a time consuming task. Digging it out would be one option but you have to make sure you have removed all the roots else the problem will reappear. You can add chemicals, but there is no guarantee that you will remove all the plants and it can take years to have a the all clear. A Japanese bug "aphalara itadori" has been introduced (2010) to the UK and is a preditor to Japanese Knot-weed, so you either need to get hold of some or hope that there are some in your area to feast on your weed.
Maybe a combination of the above will help but you definitely need to get specialist help if you think you have Japanese Knot-weed.