Soakaways

If it's their soakaway don't see why you'd have to be responsible for it. You could ask your solicitor.

Can you just refuse it? Unclaim the piece of land?

It would not impinge on access in any way as it is on a grassed area over the road from my intended house - it is a small private road leading into the estate. It is not a piece of land that I would ever plan to use in any way, and I do not have to pass over it to get into my house.

There is a hedge on the side of this piece of land, but no trees. The soakaway is newly installed.

My only concern about legally gifting it to the owners of the houses it is used by is that it will cause massive delays - 4 lots of owners and solicitors. Also I doubt if it would be a gift they would want as they might find themselves having to repair/maintain it!

Where we lived previously we (or rather our next door neighbour) had problems with our shared soakaway and it turned out to be the roots of their large conifers which had blocked it. The roots had grown into a long twisted rope.
DH and next door neighbour managed to sort it between them after the drain clearance firm failed to sort out what it was.
So be aware of any tree roots.

However, if it not your soakaway could you legally give this piece of land to your four neighbours if they are willing? Would that impinge on any of your access or rights?