The re-entry of Macquarie follows the Alinta board’s rejection of the bank’s earlier offer in favour of one from rival Babcock & Brown.

In a statement to the market, AGL said it would pay $345 million for the remaining 67% of the Alinta-AGL retail business it does not already own from Macquarie.

The deal would also see AGL sell to Macquarie its 33% interest in AlintaAGL’s co-generation assets, which comprises 280MW of co-generation and a further 351MW of open-cycle generation under construction.

AlintaAGL was formed after the Alinta-AGL merger and subsequent demerger six months ago.

This monring, Macquarie confirmed it had launched a revised proposal for Alinta, in which shareholders could choose between a full cash option, a full scip option or a thrid balance option.

Macquarie said it has provided underwritings worth more than $1.1 billion to support the proposal.

AGL managing director Paul Anthony said the acquisition would provide his company with an opportunity for growth in Western Australia, where regional demand for both gas and electricity was growing faster than elsewhere in the country.

“The opportunity to compete for residential electricity customers at a future date will provide a further avenue for growth,” he said.

“By negotiating the transaction now, AGL stands to secure full ownership of the retail assets of AlintaAGL at an attractive price whilst providing Macquarie with greater certainty for any new offer it may make to acquire Alinta.”