UK or AU for undergrad to get into IB?

Hi (first time posting)

I'm about to enter year 12 in Australia, I should get an ATAR around 97. I'm from the UK and want to go back for uni looking at Bath, York, Warwick, and St Andrews for my undergrad (math and eco everywhere except Warwick gonna apply for MORSE) but since I live in Au my parents want me to go to uni here and then go to the UK for my masters. I am planning to apply to the Uni of Sydney and ANU but is it better to go to uni in the UK especially if I wanna do IB in London? 

Thanks