Is addiction considered a disability for employment and beneftis rights?
Does it matter if the addiction is legal: say gambling or alcohol; or illegal: drugs or theft (Kleptomania)?
You didn't specify the context so I am assuming you mean for the purpose of anti-discrimination laws. If so, the definition of disability is found in Section 6 of the Equality Act 2010:
(1) A person (P) has a disability if — (a) P has a physical or mental impairment, and (b) the impairment has a substantial and long-term adverse effect on P's ability to carry out normal day-to-day activities.
Elaboration is provided in Schedule 1:
2 (1) The effect of an impairment is long-term if — (a) it has lasted for at least 12 months, (b) it is likely to last for at least 12 months, or (c) it is likely to last for the rest of the life of the person affected.
(2) If an impairment ceases to have a substantial adverse effect on a person's ability to carry out normal day-to-day activities, it is to be treated as continuing to have that effect if that effect is likely to recur.
However, this is subject to regulations made under the Act. Regulation 3 of the Equality Act 2010 (Disability) Regulations 2010 provides:
(1) Subject to paragraph (2) below, addiction to alcohol, nicotine or any other substance is to be treated as not amounting to an impairment for the purposes of the Act.
(2) Paragraph (1) above does not apply to addiction which was originally the result of administration of medically prescribed drugs or other medical treatment.
Regulation 4 provides:
(1) For the purposes of the Act the following conditions are to be treated as not amounting to impairments: — (a) a tendency to set fires, (b) a tendency to steal, (c) a tendency to physical or sexual abuse of other persons, (d) exhibitionism, and (e) voyeurism.
So, in conclusion, an addiction is a disability provided that the following conditions all apply:
It doesn't matter whether the addiction results in illegal activity provided the other criteria are met.
Just to add to JBentley's answer for completeness, as the question is tagged united-kingdom and the Equality Act 2010 does not apply in northern-ireland:-
In Northern Ireland, the definition of 'disability' is defined in section 1 of the Disability Discrimination Act 1995 as:
a physical or mental impairment which has a substantial and long-term adverse effect on his ability to carry out normal day-to-day activities.
This is supplemented by definitions of 'long-term' in Schedule 1, similarly to the law in the rest of the UK.
The regulation which affects the treatment of addictions as a disability is The Disability Discrimination (Meaning of Disability) Regulations (Northern Ireland) 1996, section 3 & 4 of which impose exactly the same restrictions as in the Equality Act 2010, namely:
3.—(1) Subject to paragraph (2), addiction to alcohol, nicotine or any other substance is to be treated as not amounting to an impairment for the purposes of the Act.
(2) Paragraph (1) does not apply to an addiction which was originally the result of administration of medically prescribed drugs or other medical treatment.
and
4.—(1) For the purposes of the Act the following conditions are to be treated as not amounting to impairments:—
(a) a tendency to set fires; (b) a tendency to steal; (c) a tendency to physical or sexual abuse of other persons; (d) exhibitionism; and (e) voyeurism.