Quote: Liane "So why do some of them i know have accountants and have to fill in their own returns etc?'"
Because they want to be careful with their money and minimise their tax liability? Because they're in the 40% bracket? Because it's not just the self-employed who file self-assessment forms? And anyone with complicated finances (bonuses, additional income from marketing etc) would be well advised to hire an accountant for tax purposes?
But they are employed by clubs. That's why, eg, clubs can be taken to industrial tribunals by players.
But the main point about their time-limited contracts is that it binds both parties, unless there's a mutual agreement to end it.
When a club gets rid of someone (player or coach) part-way through , for instance, they have to either pay up the remainder of the contract, or at least pay compensation for it, or actually sack someone, showing they've breached their contract through gross misconduct or similar.
Similarly, if a player or coach simply ends their contract part way through, the club is entitled to seek appropriate monetary compensation, whether in the form of a transfer fee or from the player directly