Cadw, the historic monuments body for Wales, is being urged to consider if more grants for Chirk Castle, near Wrexham, can be justified.

Under a legally binding agreement Cadw is obliged to fund "in perpetuity" to the National Trust the difference between the cost of running the 14th century fortress and the income received from visitors.

The �250,000 annual costs add up to 8% of Cadw's building grants budget.

Details of the never-ending contract emerge in a report by the Auditor General for Wales, Sir John Bourn.

Sir John examined the work of Cadw in protecting the 22,000 listed historic buildings and 3,000 monuments in Wales.

Concern was expressed in the report that more than 12,5000 buildings of special historical importance in Wales could be demolished unless they are listed.

Sir John said Cadw may take up to another six years to list all the relevant buildings.

The National Trust took over Chirk Castle and nearly 500 acres of surrounding parkland from the Welsh Office in 1981.

Chirk receives grants "in perpetuity"

In return the Welsh Office agreed to fund �3m in capital works as well the castle's annual "maintenance deficit".

Concerned at the rising costs Cadw later sought legal advice on the upkeep deal but was told it was legally binding.

In his report, which will be studied by the Welsh Assembly, Sir John reveals that the National Trust has accumulated reserves of some �1,224,000 at the castle and "continues to enjoy annual maintenance funding".

Yet Cadw has offered further building grants for more work at Chirk.

"In these circumstances, we believe that Cadw should consider whether further grants for Chirk Castle are justified", said Sir John.

His report reveals that last October Cadw offered a grant of �76,244 towards the �191,000 estimated cost of repairs to the main gates.

'Good value'

In a response to the National Audit Office Wales, the National Trust said the annual upkeep payments by Cadw "represented good value for money for the taxpayer".

Close to the Welsh-English border, Chirk Castle is described by the Trust as a "magnificent" Marcher fortress, completed in 1310 and occupied by the Myddleton family for 400 years.

The trust's brochure states: "The beautiful 18th-century parkland contains many mature trees as well as elaborate gates made in 1719 by the Davies brothers".