Holding of 51% vs. 75% shares
As 75% voting is required for Special Resolution (having power even to remove director), it is obvious that holding of 75% shares is the most "secure" way of securing control. However, sometimes, it is only necessary to hold 51% shares because Ordinary Resolution is good enough to "issue additional shares to non-existing shareholders". This means the % of shareholding can be changed by passing of Ordinary Resolution.
Shareholders should aware that there are rules governing how a meeting should be convened. Otherwise, the resolutions can be regarded as invalid.