definition of severely disabled person

does anyone know where I can find a definition of this, it keeps cropping up in various benefits, the latest in UC, and I am getting a bit confused. is there different levels of disabled person? (not wishing to be rude or offensive)

as always any help is gratefully appreciated

This is most obviously in reference to the Severe Disability Premium (SDP)

The SDP is a substantial uplift in the main means tested legacy benefits available to people on the proposition that they have recognised care needs but nobody to meet those needs. It can be included in irESA, ibJSA, IS, GPC and HB.

In very general terms, you will qualify for the SDP if (1) you are getting the right sort of disability benefits - usually PIP daily living, DLA middle rate care or AA (2) nobody is claiming Carers Allowance for looking after you and (3) there are no non-dependants living with you such as adult children (certain people, such as those who are themselves disabled, don’t count).

The SDP is £65.85 per week. If you have a couple, both members of whom meet the conditions, the SDP doubles up to £131.70.

Controversy arises because Universal Credit does not include any equivalent of the SDP so people currently getting the SDP are generally losing out on the switch over to UC. The High Court has ruled that the failure to make suitable transitional arrangements was unlawful, and this has led to a whole series of fudges aimed at putting matters right - the current position being that anyone who is now getting the SDP as part of their legacy benefit award cannot claim UC and is allowed to claim legacy benefits and compensatory payments are being made to former SDP claimants who were pulled into the lobster pot before the rules were changed.

Helpfully, whether you get the SDP or not is not really a comment on the severity of your disability. And the SDP should not be confused with the Enhanced Disability Premium (EDP) or the regular Disability Premium (DP) which each have their own entitlement conditions.

Section 80 of the Welfare Reform Act 2012 refers to people being limited or severely limited in their ability to carry out daily living or mobility activities, referring to the standard or enhanced rates of PIP. This seems to be the most common usage referring to benefits. I would guess that in relation to UC it is being used as a loose description of people assessed to have Limited Capability for Work and Work Related Activity.

I doubt that you will find a universally accepted definition anywhere (although I am not familiar with medical academic debate). There are medical definitions of things like severe learning difficulties, severe arthritis, etc., but whether even these are universally agreed in all cases, I doubt it. The definitions given by schools, social services, etc., will have certain similarities with the DWP world but (in my view)  it all boils down to interpretation of degrees and different opinions.  https://www.disabilityrightsuk.org/meaning-disability says broadly similar about disability