Forgot this about requiring planning permission for demolishing a house:
All advice online 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.
It is an offence to carry out any work that requires planning permission and the offence can carry very heavy fines and imprisonment. You can find out whether your work requires planning permission via a Section 5 Declaration to the Local Authority
It is an offence to demolish a habitable house without planning permission. NOTE: A habitable house includes a structure which was last used as a dwelling even if it is now in an unliveable condition. It also includes a building where the last permitted use was as a house, even if it has been in unauthorised use since. A derelict or run down building previously used as a habitable house, is still a habitable house.
It is an offence for a person to carry out either works or a Material Change of Use to which the Building Regulations apply without notifying the Building Control Authority via a Commencement Notice. The notice must be given to the authority not more than 28 days and not less than 14 days before the commencement of works or the change of use. Once validated by the building control authority, works must commence on site within the 28 day period.