planxty

I was wondering if anyone could help me! We have been living, working and paying our taxes in Spain for the last 5 years. But we have decided to move to Nicaragua to do some voluntary work, but to support ourselves we would like to do a little work. It is not worth getting Nicaraguan citizenship as we will not be there forever and it is really difficult to get. Another British friend told us that she is reg. self-employed in the UK (as it is cheaper in the UK to be self employed than in Spain). So I would like to register as self employed again in the UK without moving back the UK. Is this legal? Is it possible?

Saludos
Planxty