+1 per previous advice, but I would also contact your solicitor and ask them to check your title.
I would also notify your insurers about this occurrence - your contract may require it.
First, establish who owns the wall and then establish who is liable for repair.
Three may be additional issues such as whether it was affected by -
- Ground Movement
- Frost Damage
- Flooding
- Wind Loading
- Building Work
- Traffic Vibration
- Land Slippage
There may be a Health and Safety Issue.
This applies to public and the house occupants.
You may need to vacate the premises for a period.
An engineer should be called in to inspect by you or the council.
Re-routing road traffic well away from the affected zone of the collapse is indicated.
Temporary works may need to be carried out to restrain the earth to prevent any further collapses.
The engineer should inspect beyond the immediate area of the collapse and assess the condition of abutting structures urgently.
A services engineer or environmental officer should check all service runs and conduits in the vicinity to ensure integrity, especially gas, water and electricity.
ONQ.
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.