Even though avocados do little growing in winter....soil moisture is still very important. Tip burn can be caused by salts or lack of water. You have major burn...so I am thinking your roots got very dry at some point. Not to worry...it can recover. Just remember to always have moisture around the roots. Avocados can dry out because they are shallow rooted.

Ok could possibly be but with all the rain recently the soil looks to be very wet. It's in a pot too.

I had a similar situation and the advice I got (too late) was that Avocados "don't like cold wet feet", and that watering should be cut way back in the wintertime. I have no idea what's correct.

Hmm I'll try and let it dry out. Since the pot has captured a lot of rainwater. Thanks for the comments. Any more is appreciated

Moisture meters are quite accurate and inexpensive. I recommend getting one at HD or your local hardware store. Your damage was done probably months ago. Those brown leaves will not re-green. They will drop and new leaves will replace them next Spring. Pots must have free-draining mixes, and have good drainage holes. Do NOT let the pot completely dry out. You can not un-due those brown leaves.

The pot that it's in doesn't have good drainage so I'm most likely going to plant the tree in my backyard as it will have greater chances of fruiting there and thriving.