Damage to my property by neighbours

[Goldilocks70]

My neighbours are building an extension, which is almost finished. It included removal of a huge amount of soil and rubble, about 1m from my own extension. Now my path is all cracked and there are cracks in my external wall - and they're getting bigger. Mysteriously, one of the cracks has been filled with a silicone filler recently - and not by me! I spoke to my neighbour as we're on friendly terms but he's implying I'm fussing about nothing and denies filling the crack. I'm no subsidence expert but the cracks are new and I think he's damaging my property. What should I do? Will my council help?

[buildersmate]

Oh dear. Its a little late in the day for invoking the main legal Act put in place to stop this sort of thing.
In England & Wales the Party Wall Act has been with us since 1996, and it covers situations when undermining of foundations can cause this type of issue.
Download and read this document, especially paragraph 22.
http://www.communities.gov.uk/documents/planni ngandbuilding/pdf/133214.pdf
It is not the physical distance away that is critical, but whether they dug below the horizontal level of the base of your foundations. Being only 1 metre away, ANY undermining is likely to cause this sort of problem. I suspect that they have undermined your foundations.
This (the base level of your foundations) should have been checked before digging started.
What I am not sure about is whether the Party Wall Act can be invoked at this lat stage - the PWA enables you to get free services of a surveyor to establish that what is to be done under the Works won't damage your property. The cost of the services of the Surveyor are borne by the neighbour - not by you. I suggest that you phone a Chartered Surveyor, mention the PWA, explain what has happened and ask whether it is possible to involved their services now.
The other 'friend' you can try is Building Control at the local council. The foundations will have beed inspected before concrete was poured, and you can ask their advice. It is quite usual for BC Officers to ask questions about this sort of thing at the time - but it is not their responsibility because it is a civil matter between you and your neighbour. The BCO checks are there to make sure the new structure has proper foundations, however it is not in BC's interests to allow something to happen during the build that causes a problem next door.

[buildersmate]

(Part 2)

This is a second line of enquiry though, because BC are NOT responsible for spotting this, or what has subsequently happened - the neighbour is.

You should be concerned about it.
I hope that the Surveyor you contact advises that you can invoke the PWA then you get his services for free. Ligitation of damages is often expensive and the cost of the professionals has to be funded by you. The alternative is by a Surveyor working on your behalf to get resolution (which may involve underpinning) if your wall has been undermined.
Take photographs of the situation now.

[buildersmate]

Para 26 in the document - not Para 22.