Kristiansand99 wrote:
We have recently moved house and we have an area between our house and
our neighbour's house which you would think would be shared between
the properties. Our back garden is partly behind this area, so you
would think that that border would continue forward between the
houses and through to the front garden and the up to the road.

I wouldn't think that. Property lines are determined by the plat of the
property, which is in your local town hall property records and also on the
survey that you (and/or your title company) received when you bought the
house. You did get title insurance, right?

So look at the official records and see where your property line is.