Under the Insolvency (England and Wales) Rules 2016, a creditor must do all that is reasonable to bring a statutory demand to the debtor's attention and, if practicable, serve it personally. Where personal service is not practicable, alternative service can be used, but the creditor must be able to evidence the attempts made.
The demand gives the debtor 21 days to pay, secure or compound the debt. Only after that period expires, and where the debt remains unpaid, can a bankruptcy or winding-up petition ordinarily follow — which is why the service evidence is often scrutinised at the petition stage.