glad you got back, it can be v lonely if you don't know anyone in the UK. There is a UK support site I'm on which is a closed facebook site you can request to join. I'm not on facebook but use my sons page to chat on there. I can give you the link if you PM me.
I'll try and answer your questions, but firstly what your GP is saying sounds highly questionable, even rubbish to be frank! Most ANs are already out of the ear canal (IAC) and protude into an area called the CPA. They all cause pressure of some sort.
GPs know little about ANs in my experience as they are so rare. I know someone in Southend on the UK support site who saw a neurosurgeon at Addenbrooks and he decided for surgery. As far as I know Broomfield is not a centre for AN treatment and you may be referred elsewhere. There are only a few centres in the UK that treat ANs either with surgery or for radiosurgery, so most of us have to travel. Who are you actually seeing at Broomfield? You need to see someone with experience of ANs.
My history is I now live near Bristol. I had bad imbalance/ dizzyness and saw the ENT guy first who ordered the MRI that found the AN. I was ref to a neurosurgeon in Bristol (the major Brain Tumour centre for the South West) who said he only liked to operate on 3cm or larger as there are risks with surgery, and he referred me to oncology for radiosurgery. I was terrified of surgery anyway and wanted radiosurgery. My AN was 15mm approx then. It took 3 to 4 months till treatment (it was cancelled once, as often happens).
My symptoms got worse since, with bad tinnitus and gradual hearing loss in the AN ear, also imbalance is much worse. My AN has got bigger prob swelling, and I have to wait another year for the next MRI. But surgery can leave you with other side effects, and always carries risks. So its a difficult choice. A good neurosurgeon will go through all treatment options. It all depends on the size of the AN and your age and your own preference. Sometimes people watch and wait if the AN is small.
Your GP should have the radiologists report on your MRI, I'd ask him the size of the AN. As I say he can't possibly know the prognosis unless he is an experienced neurosurgeon!