The forward contract agreement gives Dexus the ability to acquire the underlying CPA units at $1.1334 a unit, representing a 1.5 per cent discount to CPA's last stated net tangible asset of $1.15, as at December 31, 2012.

The chief executive of Dexus, Darren Steinberg, said the investment was expected to be accretive to earnings.

Mr Steinberg was formerly the head of Colonial First State Global Asset Management (CFSGAM), which is the direct manager of the CBA's property trust.

"The CPA portfolio comprises $3.7 billion of prime-grade office properties which is consistent with Dexus' investment in high quality Australian office properties," he said.

Mr Steinberg said ''at this stage we have no intention of making a takeover offer for CPA".

''We see this as a strategic investment in a company that owns high quality office assets that are a good fit with our business.''

In effect CBA put its three, separately managed real estate investment trusts, CPA, CFS Retail and the Kiwi Income Property Fund, into play on Wednesday when it announced it wanted to internalise the management.

The REITs are managed by CFSGAM, which is under the overall CBA banner.

Each trust has its own direct management: Charles Moore at CPA, Michael Gorman at CFS Retail and Chris Gudgeon at Kiwi Income. They report to Angus McNaughton, head of CFSGAM.

David Ellis, an analyst at Morningstar, said any move to internalise the management of the trusts would require the approval of unit holders.

"At this early stage, we are positive on the internalisation proposal but we await more detail on the financial impacts to CPA, if the proposal proceeds," he said.

"We have long argued external management introduces fee leakage and conflicts of interest. Performance fees are particularly costly.

"The internalisation proposal is at the early stages of consideration and our $1.10 fair value estimate is unchanged. At current prices the fund is trading at a 3 per cent premium to our valuation."

CPA has a market capitalisation of $2.6 billion, CFS Retail's value is $5.6 billion and Kiwi Income is $NZ1.1 billion.

Pricing for a funds management business is generally about 2-3 per cent of the total assets under management, which varies depending on debt levels and assets quality.

According to JP Morgan's Richard Jones, the cost of internalisation of all the trusts could be about $650 million, based on 9.25 times earnings before interest and tax multiple, or 3.3 per cent of assets under management, that could culminate in about 2 to 2.5 per cent accretion for CPA and CFS retail.

"If CBA is to exit its investments, it may also sell its property management business or internalise management for its managed REITs.

"The CFSGAM property business manages about $20 billion in assets under management across CFS Retail, CPA, the Kiwi Income fund and wholesale funds and joint ventures," he said.

"We estimate the business generates about $70 million in EBIT and, if put to the market, could sell for about $650 million.

"While it may make sense to offload the investment stakes, the sale of the asset management platform is less clear cut. CBA makes a high about 20 per cent return on equit on the management business, with the only invested capital being $311 million in intangibles paid to John Gandel [who owns 15.5 per cent of CFS Retail] back in 2005. This compares with about 6 per cent return on equity for its [CBA] investments post-Basel III changes."