Thanks for your question.
That your father is ill in another country is not sufficiently exceptional circumstances that dictate the UKBA should give you further leave to remain in this country. An example of an exceptional circumstance would be where a father should be permitted to stay in the UK to care for his gravely ill child who does have leave to remain.
The point is that you are free to return to Spain at any time, it's just that when you do your overstay will be noted and you will probably receive a ban (most likely for a year) from entering the UK.
There is no other way that you can regularise your stay here if there are not human rights grounds which apply (other than your father - which is not relevant to securing your stay in this country as explained above).
If you return to Spain and receive your Spanish passport then you will be free (subject to any ban you receive) to exercise your European treaty rights to come and work here free of restriction
I am very sorry it could not be better news.
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