Hi bro welcome to AFN fellow UK Expat here currently in NW Spain
If they are the same plant and leaves that you posted on Monday i would swing towards Phosphorus deficiency, the fading orangish spots in Mondays pics look like it in a early stage more so so than Calcium that appear more like brown burnt spots. The latest pics looks like phosphorus at more advanced stage which is where it shows the bigger spreading blotches and yellowing out of the leaf, usually shows on the mid to lower leaves first before starting to work it way up which is where it seems to be hitting your plant.
Have you started feeding Bloom yet ? if not would convince me even more it is Phosphorus and also will be your solution. Could be PH causing it more than lack of in which case feeding more could cause more harm than good, so always a good idea to get a PH measurement of the soil when possible before committing to any solution.
Will tag in
@Waira as he is a true plant problem and deficiency guru and may swing on by when he gets a chance to throw in his
Could also always post up in the Infirmary where you should get a full set of expert eyes on the problem
https://www.autoflower.org/forums/autoflower-infirmary-for-sick-plants.90/
I sure as hell don't miss that Sahara sand dust used to be cleaning that shit for a week when i was in the South. Peace pal and best of luck going forward with the grow