Self Assessment Tax Form

altypete

I pay my tax each month through PAYE, but it appears that I might have to fill in a self assessment form as the company I work for got bought out in December and I was allowed to exercise the share option I had in the share save scheme, but because it was before the 3 years were up, it looks as if I am liable for income tax on the amount I made on them (£790).

Firstly, how do I calculate the amount I would owe? Is it a straight 20%?

Secondly, I have never in my life had to fill in a self assessment tax form. If I decided to turn a blind eye and not bother, what realistically would the chances be of anyone ever finding out?

Frankly, I don't know why I need to have the stress of all this. I'd much rather it was deducted at source in the normal way.