Well if you don't have at least ABB/AAB at A levels, then you will not be able to get into a bank. In which case it is pointless obtaining an expensive masters degree over work experience. If you do have the minimum grades, the best thing to do is network if you want to work in a bank somehow and undertake a masters if affordable - but this may be to no avail. The other options are to apply for IDBs and move sideways, or trade support roles in the buy-side, or just to go into prop trading.
You haven't mentioned what you want to trade. What asset class are you interested in?
In order to stand out, yes, you'll need some financial experience - if you're really into markets I would suggest starting a blog or trading your own account if you have some money set aside.
But for your average guy, it's hard to afford the masters and/or trade on your own - so i'd look at doing some prop trading work at the very least.