The film is based on women in Rylstone, Yorkshire

Starring Helen Mirren and Julie Walters as Women's Institute members who stripped off, it took almost �1.8m in its first weekend on full release.

It knocked Pirates of the Caribbean - which earned �1.2m - off the top spot.

The film is based on women in Rylstone, Yorkshire, who produced the calendar for leukaemia research in 1999.

And it is widely expected to be one of the most successful British films of the year, in the mould of The Full Monty and Billy Elliott.

Although �1.8m is not a blockbusting total, film-makers are hoping it will have lasting popularity among older fans.

UK BOX OFFICE TOP FIVE 1. Calendar Girls - �1.8m 2. Pirates of the Caribbean - �1.2m 3. American Pie 3 - �660,000 4. Tears of the Sun - �410,000 5. Jeepers Creepers 2 - �380,000 Source: Screen International

Walters plays Annie Clarke, whose husband dies of leukaemia, while Mirren is her friend, Chris, who comes up with the calendar idea.

In real life, the calendar sold 300,000 copies and raised �500,000 for the Leukaemia Research Fund.

Film giant Disney, which made the film, has already given donations to the Leukaemia Research Fund and the real-life WI women have agreed to give their royalties to the charity.

But its first weekend takings are overshadowed when compared with other summer comedy hits - like Bruce Almighty, which took �7.3m, American Pie 3 with �4.15m and Pirates of the Caribbean with �3.8m.

Elsewhere on this week's chart, Bruce Willis' new war movie Tears of the Sun could only enter at number four, taking just over �400,000.

And Heath Ledger thriller The Sin Eater - which flopped in the US under the name The Order - went in at number 10, with �162,000.