To join JustGiving you need either a charity registration number or a Gift Aid reference number. Even if your church or parish is exempt from registering as a charity, you'll still need a Gift Aid number to join JustGiving.
If your church does not have a charity registration number or a Gift Aid reference number then they aren’t able to join JustGiving. This is because we need to be able to verify the organisation with an official body (such as the charity commission or the HMRC) for security reasons.
It is not possible to register using your Diocese or umbrella association's charity number or Gift Aid number.
To learn more about getting a Gift Aid reference number from the HMRC visit http://www.hmrc.gov.uk/charities/tax/recognition.htm