As an employee your contribution to National Insurance will be deducted from your base salary by your employer. He also pays his own contribution on your behalf. Up to a salary of €2,652 your contribution will be 4.7% of your salary against general contingencies and 1.6% against unemployment. 

Being Self-Employed 

If you are self-employed your contributions will be in the region of 28.3% of earnings over €740 per month. You can elect not to be covered for short term incapacity in which case you will pay only 26.5%.

Transfer of Benefits from the UK

One aspect of the social security system in Spain that often comes up is whether or not benefits that you are entitled to in the UK can be transferred to Tenerife. In the case of unemployment benefits - if you have been receiving it already for more than four weeks, you may be entitled to continue receiving it in Tenerife for up to three months. For more information about this and other benefits including pensions you can contact:

D.S.S.-Overseas Branch
EU Office Longbenton
Newcastle upon Tyne NE98 1YX
Tel: 0191 213 5000

There is a leaflet entitled "Social Security in the European Union" published by the European Commission which is full of useful information. You can request it from the address above.