First thing to clarify is that Supplementary Welfare Allowance i.e, Basic payment is payable pending a decision from Social Welfare - other wise it defeats the purpose i.e having income pending outcome of application. But it sounds like your claim has been refused on the habitual residence condition which is applied to all citizens alike, irish and non irish. If you do not have a continuous two years residence in Ireland they will refuse payment. However, there are another 4 factors (centre of interest, future centre of interest, length of absence from the state and record of employment in the state) to take into consideration and you should appeal the decision. You basicially need to prove you are here and you are here to stay so family connections in Ireland and links to the community would be important. Record of any attempts to secure employment here would also be important.
Something that might prove helpful would be if you got one week's insurable employment (pay a prsi stamp) this would acitivate your social insurance record from UK and you should qualify for Jobseekers Benefit which does not require that you meet the habitual residence condition...
HTH
A