http://www.legislation.gov.uk/apni/1969/16/section/2Theft Act (Northern Ireland) 1969An Act to revise the law of Northern Ireland as to theft and similar or associated offences; and for purposes connected therewith.texttext/xmlenStatute Law Database2023-03-302009-02-02Definition of “theft”
2“Dishonestly”.(1)

A person's appropriation of property belonging to another is not to be regarded as dishonest—

(a)

if he appropriates the property in the belief that he has in law the right to deprive the other of it, on behalf of himself or of a third person; or

(b)

if he appropriates the property in the belief that he would have the other's consent if the other knew of the appropriation and the circumstances of it; or

(c)

(except where the property came to him as trustee or personal representative) if he appropriates the property in the belief that the person to whom the property belongs cannot be discovered by taking reasonable steps.

(2)

A person's appropriation of property belonging to another may be dishonest notwithstanding that he is willing to pay for the property.