It's really important that you check with British Citizen Services before you send your application to the Home Office. You need to make sure that you've filled everything out correctly, and made sure that you've ticked all the right boxes. If you apply and then realise that you've missed something, you can't just send another application in.
After applying at a Post Office branch you can track your application. You used this service if: the Post Office took your photo for you. your application reference begins with 'POD'