Happy to see people read my questions
Sorry for my late reply, I was dealing with a lot of stuff, including a 80% total account value loss with Bitcoin (Just an advice, stay away from it. Or at least do the opposite of what I do).
Regarding why Options on Index vs SB the index itsels, it is clearly subjective, but a combination of Selling an option in the money, Buying the opposite out of the money, and SB the index is the one that during reversal gets me the best reward with the lowest margin.
Iam in the process of getting an IB option account, as SB on shares is usually not extremely convienent to me, big spreads, low leverage, etc etc.
And yes, they have asked me the NI as well, so I don't think is related on big wins or not, it is more to confirm your being a UK resident (I think). They have also asked me for Passport details.
My understanding is that, provided that you have a job/additional income, it cannot qualify as your main occupation and therefore cannot be taxed.
PS: Anyone of you guys on IG and using the iOS app last version on an iPhone 6? In that case do me a favour, try to open the chart of any option (let's say SP500 weekly 2500 call), does it visualise ok or does it get stack at the loading page?