I'm not a big fan of using date for ID but Mallow Skipper flies early (I have seen it in late January and February in Málaga province where it can be seen throughout the year) whereas Southern Marbled is a later species - predominantly seen in May and June but I have seen them in the last third of April.
Page 28 of the pdf that Timbirder3 linked is good for showing the differences.
Thank you, Paul. Great feedback. Now that you mention it, those 'translucent cell-spot narrow' as described in page 28 are also there on my photograph. Thanks again to Timbirder3 for the excellent guide. Cheers.