A conclusive presumption (also known as an irrebuttable presumption) is a type of presumption used in several legal systems.
In English law, a conclusive presumption is a presumption of law that cannot be rebutted by evidence and must be taken to be the case whatever the evidence to the contrary.
For example, the doli incapax rule conclusively presumes that a child less than ten years old cannot be held legally responsible for his or her actions, and so cannot be convicted of committing a criminal offence. The age was seven at common law, and raised by the Children and Young Persons Act 1933 to eight (section 50) and by the Children and Young Persons Act 1963 to ten. A similar rebuttable presumption, that a child between the ages of ten and fourteen was not capable of committing a criminal offence, was abolished by the Crime and Disorder Act 1998. Now the age of criminal responsibility in England and Wales is 10.
The new addition to the Crime and Disorder Act 1998 (c. 37) states
See also the case of R v JTB [2009] UKHL 20. Despite obiter comments in the earlier case of Crown Prosecution Service v P [2007] EWHC 946 (Admin) (27 April 2007), doli incapax as a defence and as a presumption for children aged 10 or above was abolished by section 34 Crime and Disorder Act 1998.