Basically, we must deal with a contract signed between a professional (Bank) and a consumer, the clause has not been negotiated in an isolated way (that is, imposed by the bank) and it causes recognized damage to the client (a higher amount due to this ground clause).
Therefore, the above mentioned Sentence referred to the demand of a double control of transparency in the transaction. The first control deals with the inclusion, in the sense of writing clauses, written in a clear and understandable way and, in case of doubt, the interpretation favourable for the consumer will have to prevail. The second control refers to the content, as those clauses that have not been negotiated in an individual way and cause important damage to the consumer will be considered unfair.
It is essential to highlight that although some inferior courts were admitting the retroactive effect since the loan contract, applying the logical theory of what is invalid can not have any effects, the most part of the courts which face these type of claims, nowadays, establish that the date of nullity of the clause is 9th May 2013.
This restriction will probably disappear after the statement of the Court of Justice of the EU dated 21/12/2016 indicating that there is no limitation to the retroactive effect that the Spanish courts have been applying.
Therefore, it is now foreseeable that the judicial statements declare that if the clause is invalid, it is not able to cause any effect, so the Banks must give back all the money improperly charged by the implementation of the ground clauses.