I'm not an expert but I think the following is correct:
The basic principle is one share one vote so one shareholder with 500,000 shares voting "yes" will defeat any number of shareholders holding 10,000 shares between them voting "no".
Above assumes the vote goes to a "poll" as opposed to voting on a "show of hands" but any shareholder can insist at the meeting that the vote goes to a poll.
As to the number of shares you hold (which you dont fill in on yoour proxy form, the company's share register tells them how many shares you hold. The relevant "snapshot" date is usually a day or so before the date of the meeting.
