I am from Mexico and I intend to start postgraduate studies in the UK later this year. I am going to apply for an ATAS certificate this week, which means I will get it around mid october (hopefully). The problem is that I already had a flight for september 22nd because I thought I would get my visa faster (I was too naive).
Anyway, to elaborate my question a little more, can I travel to the UK as a tourist while I wait for my ATAS certificate and then come back to Mexico to get my tier 4 student visa? As far as I know, we mexicans don't need a visa to visit the UK (correct me if I'm wrong please) but I don't know if I could get in trouble for traveling as a tourist, then leave the UK and come back around two or three weeks later as a student, so any advice/help will be greatly appreciated, thank you very much.