Why can’t I vote online for the UK General election?

If the internet is secure enough for everyone’s money and bank accounts (and has been now for 10years already) why are we still using old fashioned voting? And it can’t be about ‘verifying your identity’ – I do postal voting now and it would be way more secure than that surely – people could not intercept my ballot for one thing.

Best online voting system? How does it work?

What is the best online voting system that will make users comfortable? Each user should be unique individual and each vote as well. People like to make many accounts and vote using each account. What is the best way to avoid such scams?

Ideas:
Credit/Debit Card information (Most likely uncomfortable but the best proof)

Phone Verification (Well, what if there is only the home phone but 5 users in the house?)

Picture Code Verification (Pain in the neck just to vote someone)

Home Address (How does this really show you are unique? Show if it match the Internet ID address? Anyone can fake a home address)

Computer ID (Okay, like, 5 users per ID? What if there is a computer with different IDs such as Library computer or a computer lab in college/school? Hackers know how to make instant new instant IDs)

Internet ID (Yes, but usually that is one ID and what if there are many computers with one ID? This mean that only 5 users per ID? What if this is a college computer lab and students go in, is there multiple IDs?)

User Score (Activity, votes, reviews, etc and the score and votes or something is calculated to get a score and the highest score is the best chosen?)

Email Verification (Yes, but it is easy to create many email accounts)

Multiple Verifications (That means the cheater will have an opportunity to make multiple accounts)

One Vote per 24/hr (What if I have 5 users on this computer, that mean only one person can vote out of the 5?)

One Vote per until expiration (Sounds good but how do I avoid multiple accounts of the same cheater?)

Please read to the bottom..

What is your thoughts? Remember, the user is comfortable and the voting system is fair but complex to avoid cheaters.
I am trying hard to figure out how some companies create such complex but fair voting systems (they keep as a secret) making users comfortable. Its science, art, and interesting.

Why can’t we vote online for the general election?

It kills 2 birds with 1 stone – cuts costs by eliminating voting personal and also eliminates paper, and I would tend to think that “voter turnout” would also drastically increase.

So what’s the real reason why?