As a creditor, do not in any way authorise or request payment by posted cheque, unless you are happy to bear the risk of loss (the risk is yours as soon as the cheque is posted).  Rather insist that your customers make payment direct into your bank account, and/or that - if they choose to pay by cheque – they do so at their risk entirely.  Take advice if you aren’t sure that your credit documentation covers you adequately in this regard.

As a debtor, if you post a cheque and it is stolen, you will still have to pay the creditor all over again unless you can prove a prior, clear agreement (actual or implied) by the creditor to take the risk.  Don’t assume that a creditor has consented to your paying by cheque just because your cheques have always been accepted in the past – failure to object cannot amount to an agreement to accept the risk. 

And, per a recent High Court case, this principle applies to all modes of delivery, not just post.  Thus in the case in question, a cheque was intercepted after it was forwarded via a document delivery service (akin to a courier service), and risk was held to have remained with the debtor because it had chosen the method of delivery.