Nothing if you have less than 4 employees apart from EL insurance, after that all you need is an health and safety policy.
The more prudent will give h&S training , even if it is provided by yourself. then get them to sign a rules sheet, stating what they can and cant do, ie no ladder to be climbed unless it is at least, tied , footed etc.
have they been shown how to climb a ladder , (3 point of contact rule) etc
The Hse website has all the info you need
Dave