Who's selling?, page-84

They don't need any shareholder a T/O offer. They also don't need to notify anyone until they get to 19.9% as a substantial holder (initial sub holder notice at 5% then every 1% increase).

A T/O can be either a friendly one or a hostile one. A friendly one comes with support of the board and is nearly always successful as institutions follow the boards advice.
A hostile bid is made via announcement to the market then they are first in line at X cents for all shares that get sold at that price. If the market rejects the T/O bid the price goes higher than the bid and stays there.
A game played by many in doing a T/O is short the company pushing the SP down then making a decent offer 30-40% above the artificially low price. Look at the recent history of PNA for what happened there.
There is a lot more about the games in T/Os but the above is just a start.