"Male sperm counts are in freefall - are we witnessing the end of humanity?" asks the venerated population theorist and geneticist Toyah Willcox.

As the lady herself - who plays a doctor here - once so memorably opined: "It's a mystery" ...but hope is at hand (so to speak) in the form of dating agency phone operator Eamonn Manley (Marshall).

He was a reluctant virgin until he"dunked his biscuit" with good time girl Mary Mallory (Tara Lynne O'Neill) with miraculous results.

Despite insisting on a chemist's counter-full of contraceptives, Mary found herself in the family way... and Eamonn's destiny as a donor is sealed.

His reputation for sperm "like tadpoles on speed" is soon spreading through Belfast and he's much in demand as a seed donor for Catholic wannabe mothers.

However, this doesn't go down very well with Protestant hardman Mad Dog Billy Wilson (Nesbitt), who reasons Eamonn's miniature population explosion will mean the Catholics are in the majority.

The thug, who is given to pursuading people to remind him how feared he is by making them read out a newspaper clipping he carries around, is also slightly miffed about Eamonn's courtship of funeral parlour worker Rosie (Kiera Clarke).

She knows nothing about his daytime business of realising the dreams of childless couples but he can't keep a lid on it forever.

Director Dudi Appleton breathes lifes into this ludicrous storyline by lending it a slightly cartoonish quality and keeping the plot rolling along at breakneck speed.

Marshall, who is probably best known to British audiences as Robert Lindsay's son in the tepid BBC sitcom My Family, invests what could have been an irritating twit with a wide-eyed vulnerability.

However, it's the small details, particularly the lampooning of Catholic and Protestant bigotry, that provide the most satisfaction.

In the style of grafitti tributes to UDA or IRA heroes, a mural of Gloria Hunniford looms resplendent while a notice in the office reads: "Punishment beatings will continue until staff morale improves."

Tim Evans