during our BR my wife recieved a bonus from work and my Grandmother died leaving me £1,000 in her will - as we do not have an IPA and do not want to jeapordise that fact we have handed both amounts over to the OR - just not worth not doing.
If you are undischarged then once you receive the cheque mention it to the OR. They may decide that you can keep it as it is a one-off and not a huge amount of money or they may want to whole amount.
If you have been discharged you don't have to advise the OR of any windfalls so you can spend it on whatever you want.