The giant investment firm behind a private multibillion-dollar airport rail plan has written to Labor MPs in Melbourne’s west, in a desperate last bid to convince them their plan has merit.

A last-minute bid for a private rail tunnel to the airport argues anything else is second rate

IFM Investors on Monday wrote to government MPs outlining its argument for why their airport rail plan – which includes a new tunnel from Southern Cross Station to West Footscray – should be adopted by the Andrews government.

The government appears increasingly unlikely to back the private bid, with The Age this month revealing it is leaning towards running airport trains via the yet-to-be-completed Metro Tunnel.

The government would save billions of dollars if a dedicated new tunnel was not built for airport trains.