Viking
It is not confusing at all if you read the information that is sent with your E106.  This quite plainly tells you to take the 106 to the Social Security Office.  You do not take it to the local surgery (they don't know what it is), you do not take it to the Cat Salut office in Tortosa (they will only tell you to take it to the Socail Security office (INSS).  This is next door to the Cat Salut Hospital / Clinic in the Ferreries area of Tortosa.  They will take the forms off you and get in touch with the Pensions Service in Newcastle who will confirm your rights back to them.  You will receive a letter / form back in due course telling you the date until which you are entitled to receive health treatment.  You then take this to the doctor's surgery to register with Cat Salut.

No problems at all - we have done it !!