WILL MY EMPLOYER KNOW IF I START A BUSINESS?

That is weird, thats non of my employer's business. I do whatever I want out of my working hours. My current manager even knew of my business in an interview and wasn't bothered by it at all. No one should as long as that doesn't affect other job

I have a question, I trade indices and FX it's currently a self employed role and I have a big payout coming after 3 years of trial and error. My question is that after I file for self assessment as a sole trader due to it being above the £1000 allowance should I report money lost to brokers and prop firm fee expenses from previous years, is there any purpose in this? Or is it only relevant for the current tax year what my expenses were?