DH has just returned from a fruitless trip to the Passport Office, with rejected applications. It seems that the rules have now changed regarding countersignatories, and this is not made clear on the application form.
Not only must your countersignatory be a professional person from the suggested list, they have to know you as a friend/neighbour/colleague, not professionally. So, you can't ask your doctor/dentist/teacher etc to sign it unless you know them personally. Which makes the whole thing even harder. Our dentist signed for the children, and he actually knows them very well, but because he stated he was our dentist, it's been rejected. Sooo frustrating.
If you didn't realise this, like me, I hope I save you from an easily-made mistake.