As you may be aware, those with severe disablement will be pushed into the Support Allowance group with no conditionality.
There is no definition I can find as to what "severe disablement" means here, who decides this and what criteria is applied. I submitted a request for further information on this to the DWP, yesterday.
However, with respect to severe conditions, Lord McKenzie of Luton the DWP minister in the House of Lords was asked a question on ME during the Welfare Reform White Paper statement he made and it maybe relevant.
Here is the point from http://www.theyworkforyou.com
"The Countess of Mar (Crossbench) Link to this | Hansard source
My Lords, who is responsible for making a decision about what is a serious condition? The noble Lord probably knows that I am going to refer to the ME community. At the moment, they are absolutely terrified of anything to do with social security benefits, because they fear that they will be made to go to work or to do cognitive behaviour therapy or graded exercises to get themselves better, when they know that the extra stress involved is likely to make them more sick.
I remind the noble Lord that both the Chief Medical Officer and the National Institute for Health and Clinical Excellence recognise ME as a serious condition in line with multiple sclerosis and motor neurone disease. Far too often, ME people are made to feel that they are the scum of the earth, that they are scrounging and seeking attention. Please can I have a reassurance that these people will not be forced into employment when they cannot maintain it?
Lord McKenzie of Luton (Parliamentary Under-Secretary, Department for Work and Pensions; Labour) Link to this | Hansard source
My Lords, I believe that I can offer that reassurance. On the fundamental question of who decides, medical advisers are contracted to Jobcentre Plus who undertake the assessments for the purposes of the employment and support allowance. Certainly, if judgments are made that people are not able to engage with work and do not have the capacity to work, they will be put in the support group and there will be no conditionality attached to them. There is a broader issue around people with fluctuating conditions, and it is important that those who are engaged in these assessments are knowledgeable about these things, and we believe that the people who we use are knowledgeable. The noble Baroness raised that specific question on a previous occasion. Perhaps I can write to her further on that."


John hi,
Under this topic I found that the SDA was discountunied in April 2001 in financial terms. See the relevant link:
http://www.direct.gov.uk/en/DisabledPeople/FinancialSupport/OtherBenefit...
In a possbile answer to your question I found:
http://www.dwp.gov.uk/advisers/db1/esda.asp
http://www.dwp.gov.uk/medical/med_conditions/a-z.asp
http://www.dwp.gov.uk/advisers/hb5/sda/sda_1.asp
http://www.dwp.gov.uk/advisers/hb5/
Incapacity for work
You are regarded as incapable of work when you are not working because you are either physically or mentally disabled or suffering from a specific disease or condition, which includes mental illness and/or a learning disability. There are procedures for assessing incapacity for work. [Legislation (38)]