For the last few months a hole has appeared in neighbours garden next to the boundry wall about 7 foot long 3 foot wide and currently about 15 inches deep , have dug down a foot or so after another neighbour said it might be a rat warren no sign of tunnels or angry rats,it doesnt fill with water when it rains,and doesnt appear to be an old tree as no signs of old roots visible, so any ideas, its about 25 foot from a property.

Call someone at the council and ask them to look into it?

Is it on a slope? Probably an underground watercourse about to cave in. You’re doomed.

Any pics?

its on flat ground, not got smooth sides like a trench, just crumbly sides

Seen his wife recently?
If he’s called Lars, buy a flashgun.

leaking water pipes/drains can create voids any pipes thereaboots?

Mine shaft

Keep an eye on local news bulletins in Australia / New Zealand, for an elderly gent puzzled by the 7′ x 3′ x 15″ mound that’s appeared on his lawn.

its either his wifes collapsed coffin or its the entrance to an indian death cults burial chamber. I’d consider moving.

It could be a sink hole, or it might be some thing else entirely. If you can find out what your underlying geology is you’ll have a better idea.

Probably backfill to services, or some other backfilled excavation. The heavy rain we’ve had recently can induce settlement of the ground.

You’re effed! 😯

If you’re in Britain the British Geological Survey free mapping is here. It might not help much but it shows mines and boreholes

My 2p; collapsed soakaway?

Probably of no relevance but the other day, whilst randomly browsing I stumbled across (not literally of course)the Hell Hole of Turkmenistan. I couldn’t believe that there was either such a place or that I hadn’t heard of it before…

Images

If you/they still have the surveys for house purchases it will show if there is a water main/sewer underneath.

Or of course, it sounds like the right size for a grave 😯 Maybe the neighbour never got round to finishing his new patio?!

That Door to Hell is amazing!

about 7 foot long 3 foot wide and currently about 15 inches deep

Sounds like they are preparing a shallow grave – have you said or done anything to upset them recently?

What part of the UK are you in? Depending on the underlying geology it may be a number of causes. If its the midlands then Coal Mining / limestone mining is a very real issue. Derbyshire and north then Limestone Karstification can lead to some very large sinkholes.