ASR = Administrative Silence Rule.
Put simply. The developer applies for the Licence of First Occupation* to the Town Hall. If they hear nothing after 3 months has lapsed then the developer can assume legality by the ASR rule. This has worked for years where there were no illegal planning issues. BUT.. where there are irregularities with the Building licence and it has been revoked, (as is the case in Marbella) the developer cannot assume legality with the ASR.
Many of the developers in and around the CDS choose to ignore this fact and pressurise people into completing on illegal developments saying they have the *LFO!