It's Melbourne's most prestigious and expensive office tower.

Luxury retailers Cartier and Harrolds ply their trade next to its famed free-standing Parthenon-sized Doric columns on the plush marble ground floor while high above, well-paid financiers from an A-list of top-tier merchant banks contemplate sweeping south-facing views over the Yarra River.

The owner of 101 Collins Street is fighting to hold on to its million-dollar views. Credit:Jesse Marlow

However, like many in development-dazed Melbourne, 101 Collins Street is fighting – and, so far, losing – a battle to protect its best asset: its million-dollar views are threatened by a 43-storey usurper next door in Flinders Lane.

Upsetting the establishment's status quo are plans for a soaring mixed-use tower by little known company Hamelin Pipe, a business controlled by private investor Peter Hart of Bowens timber and hardware fame.