l2020

Hi all, hoping for some advice! I recently relocated back to Australia after a number of years in the UK, I am Aussie PR - my employer in the UK who I have been with for a number of years offered me to keep my job and work remotely from Australia, which I thought was great. I was somewhat prepared for the potential that I would likely have to pay double tax for a period of time until i could sort any tax issues out or claim tax back from either the UK or Australia etc, however the reality of the amount they are planning to withhold has really shocked me. My employer sought advice from a tax consultancy firm to work out any tax liabilities and have just advised me the amount that they will be withholding, its 80% of my current take home pay after UK taxes & NI. its a ridiculous amount of money, it just doesn't seem right at all. Before I challenge it with them... or just straight up quit my job I need some professional advice on what i'm able to claim back if anything or advice on if what they are taking is actually accurate. Any help from someone who has faced a similar situation or has any recommendation for UK/Australian tax expert would be great. Im aware i should of done more research into this before accepting the offer and leaving the UK, our opportunity to fly out here came sooner then expected so we took it and everything else on the priority list went onto the back burner unfortunately!