Do I need to send diplomas with my application?
No, these will normally be requested at a later stage.
Should I supply references, letters of recommendation or proof of good conduct?
Referee contact details should be supplied on the application form or listed on your CV. The employer will check the information you have provided with your referee. It is best to use your most recent employer, but make sure he/she can respond in English. Letters of recommendation are usually not needed.
Jobs in the security industry or with vulnerable people (children/elderly people) will require proof that you do not have previous criminal convictions (Disclosing and Barring Service check).