Upvote:3
I have just gone to Heathrow T2 to pickup the phone on the left and be given a very straight forward answer.
As an Australian who was naturalised on Tuesday, I am allowed to fly out on the Friday with my Australian Passport, BRP and naturalisation certificate and on re entering the UK on Monday, still within the 5 days to send the BRP in they shall take my BRP and confirm my naturalisation and let me in the country.
Why, why did I have to stress and waste hours on the phone and read endless forums.
Upvote:10
You will have two points at which your documentation is checked. First, your airline will check whether you have the correct documentation for entering the UK. Since you have an Australian passport, you are allowed to travel to the UK visa free. So you are in the clear here.
Once you reach the UK border, it is now your choice how you want to present yourself. Unlike some countries, the UK does not require that its citizens enter the country on a passport which it has issued. However, if you are presenting yourself as a British citizen who intends to remain in the UK indefinitely, you will need to provide evidence. This doesn't need to be a passport. A citizenship certificate will likely make this process very smooth, but it could in principle be anything that can convince the border force officer that you are a British citizen.
If your visit to the UK is short, then you could choose to present yourself as an Australian on a visit, fill out a landing card, and you will likely not face any further scrutiny. However, if the border force officer suspects that you will not comply with the conditions of visa free travel, then you may put yourself in the position of needing to prove that you are a British citizen.
To be safe, you ought to bring your citizenship certificate.