Government plans to introduce changes to the opening hours of heritage houses and gardens availing of tax relief spell busier weekends for the owners of many of the Republic's finest homes.

Some 120 properties of significant architectural and historic interest open to the public each year, giving their owners the right to avail of tax relief on money spent on their repair, maintenance or restoration.

The familiar names of the old Anglo-Irish gentry are among those eligible for such tax relief, according to the Revenue's latest list of qualifying properties.

Lissadell House in Sligo, home of the Gore-Booths, Desmond Guinness' Leixlip Castle and the Earl of Mountcharles's home, Slane Castle, feature on the list along with Russborough House in Co Wicklow and Glin Castle in Co Limerick, home of the Knight of Glin. But the landed classes have been joined in recent years by many people from other walks of life.

Well-known business figures who are entitled to the relief include Ryanair chief executive Michael O'Leary, whose home, Gigginstown House in Mullingar, is open in the morning from Monday to Friday from the end of March to the end of June, according to information published by Bord Failte last year.

Cathal, Declan and Shane Ryan, sons of Ryanair founder Tony Ryan, are also eligible for the relief for the Lyons Estate in Co Kildare where the house and gardens are opened for periods in February, May and September.

Other familiar names on the list include the Gaiety Theatre in Dublin, wine merchants Woodford Bourne's warehouse in Cork and Barringtons Hospital in Limerick.

Labour TD Liz Mc Manus, whose home at Martello Terrace in Bray is open in the afternoon on Tuesdays and Thursdays, is also on the list.

To qualify for relief, the houses and gardens must first be deemed to be "of significant historical, architectural or aesthetic interest" by the Minister for Arts, Heritage, Gaeltacht and the Islands.

They must then satisfy the Revenue Commissioners that they provide reasonable access to the public.

At a minimum, the properties must be open to the public for a period of at least 60 days in any one year, including not less than 40 days during the period from May 1st to September 30th. Opening hours must be at reasonable times and daily viewing times must be at least four hours.

Owners are allowed to charge an admission fee but the Revenue stipulates that it "must be reasonable so as not to preclude the public from seeking access to the building/garden".

While the Revenue does not set a ceiling for the entry fee, Bord Failte's 1999 list of such properties shows that fees generally range from £1 to £5 for adults but some premises offer free access or donate the money raised to charity.

However, there have been concerns that many of the houses and gardens open at inconvenient times when the public at large is not in a position to visit. While the larger ones boast extensive opening hours, some of the smaller ones do not open at all at weekends, opting instead for weekday mornings or afternoons when many people are at work or school.

The other main criticism of the scheme is that details of approved buildings or gardens are often not readily available to members of the public.

The Revenue stipulate that opening times must be advertised in local or national media and that a sign should be erected outside the property indicating the opening hours but both these methods of publicity can be easily missed by the visiting public.

Meanwhile, Bord Failte is not obliged to promote such properties although it is required to publish a register of houses and their opening hours. But because it is notified by the property owners before the Revenue makes its determination, the tourist board's list can end up containing the names of houses and gardens that do not go on to secure Revenue approval and end up not opening to the public.

In an effort to address these two issues, the Government has decided to insist that such approved properties open on at least 10 weekend days from May to September.

To improve the information available to the public, the Revenue will supply Bord Failte with its list of approved buildings and their opening times for use by the board in its tourist publications. The Revenue will also publish the list separately.

The new measures will be contained in the Finance Bill and while they should ensure that the taxpayer gets "more bang for his buck", they will inevitably cause difficulties for some of those currently availing of the relief to pay for the upkeep of their homes and could lead to the closure to some of them.

"I think it will create problems, not for the big homes where they have staff and are making money," says one home owner.

"The people it will turn off are those with small properties or gardens who see it not as a money-making concern but as a means of covering their costs. It will shut down some places that are currently open."

Homeowners with young families are expected to find it difficult to organise visiting hours at the weekend while the smaller operators are also likely to have trouble finding staff to ensure access on a Saturday or Sunday.

One elderly homeowner, who shows her house and gardens in the mornings from Monday to Thursday, says that she would find it impossible to open at the weekends.

"If the new measure comes in, I would probably have to give the whole thing up."