Further payments for security and gardening for the untenanted property total almost $3000 every month.

Documents obtained under freedom of information rules by the ACT Greens show vandals have been gutting the property and security costs have exceeded $110,000.

Chief Minister Jon Stanhope said he expected the property to be let in March next year.

He denied allegations that the Government had mishandled the project by letting the historic cottage fall into ruin. But the Greens say the episode has been mismanaged from the start.

Mr Stanhope said the house, which currently stands in the middle of a construction site, could not be let because of the surrounding development.

''We did significant works. We almost gutted and replaced the interior,'' he said.

''My understand is that it couldn't be tenanted sooner.''

The Farrell family was evicted from the property after the ACT Government accused them of squatting, but the Farrells maintain they were given the keys as caretakers of the cottage.

They admit they did not pay rent but invested $75,000 of their own money to refurbish the vandalised property and stop further damage.

Greens leader Meredith Hunter said ACT taxpayers had to foot the bill for the Government's blundering.

''The cost is not just monetary; the cost is also the cost of the heritage and the loss of heritage through vandalism,'' she said.

The freedom of information documents show the security company hired to protect the building has encountered difficulties.

''... security have advised that the break-ins at Stromlo are occurring at a regular time. They are simply waiting for the guard to leave then going in,'' the documents said.

Ms Hunter said, ''I think it would have been a better solution to have the Farrells to stay on the understanding that it may be used as a community facility ... my feelings are that the property would have been well maintained and safeguarded until there had been a decision about a future tenant.''

For more on this story, including comments of the Farrells on what they describe as "institutionalised vandalism", see the print edition of today's Canberra Times.