What's the risk you're seeking protection against?
A bank deposit is a debt due to you from the bank. If your bank fails, your claim against the bank for the return of your deposit is worthless. Deposit guarantee schemes mean that the state steps in and pays the bank's debt to you. (The state doesn't do that primarily for your benefit, incidentally, but to maintain confidence in the banking system, because if there's a crisis of confidence in the banking system the state suffers.)
Investments bought through a broker are different. If your broker fails the stocks, bonds, etc that you bought through that broker still exist, and are still worth whatever those particular stocks and bonds are worth. There may be a bit of an adminsitrative hassle in getting them into your hands from the now-insolvent broker, but you shouldn't have lost them.
Where you do have a risk of total loss is where your broker's business has been conducted fraudulently or dishonestly, and the stocks and bonds you bought have been stolen (or, they were never bought in the first place, and the money you paid to buy them was stolen). This does happen, but very rarely. SFAIK there's no state-backed guarantee scheme that will cover you against losses of this kind. There's fairly robust regulation in place to try to ensure that this won't happen, but in the end of the day the state can't guarantee that people won't break the law. So if your stocks and bonds are stolen and the regulation failed to prevent this, you won't get compensation from the state any more than you would if your wallet was stolen and the laws against theft failed to prevent this.