High Peak Liberal Democrats

The health minister Jane Ellison stuck faithfully to her brief. Mitochondrial donation, vulgarly known as the "three-parent" baby technique, is not genetic modification and will not lead to the "slippery slope" of designer babies, Ms Ellison insisted.

Lining her analogies up in a row, she pointed out that mitochondrial transfer from a donor egg to a patient's egg is like replacing the battery packs of the cell, which means there will be "light at the end of the tunnel" for families affected by mitochondrial diseases.

Never mind her one inexactitude when the minister eventually replied to a question about whether mitochondrial donation will be tested on monkeys before being applied to humans.

Yes, she could confirm that a technique known as maternal spindle transfer had been tested on primates - unfortunately without clarifying that the technique to be used in Britain is called pro-nuclear transfer, which was not in fact going to be tested in the same rigorous manner.

Similarly, the shadow health minister Luciana Berger kept strictly to her notes, re-iterating the line that any new medical advance is a "leap of faith" because of the small risks of something untoward - in this case the rather frightening possibility of permanently damaging the health of future generations of children.

However, Ms Berger was clearly stumped when asked to confirm whether it was possible for the genes of the cell nucleus to cause mitochondrial diseases, which would mean that not all mitochondrial conditions would be eliminated by mitochondrial transfer. (The answer, Ms Berger, is yes.)

A few years ago, not many members would have heard about mitochondria, let alone be able to explain the function of these little "organelles" of the cell cytoplasm - the bit outside the central nucleus where the chromosomes hang out.

The battery pack analogy is one we have all used, but as any mitochondrial scientist will explain, these minute structures are far more complicated than merely being mini-stores of chemical energy. They actually carry out the vital task of converting glucose to something called ATP, which is the universal energy currency of each and every cell in the body.

Thank heavens for Julian Huppert, the brainy former research scientist and Liberal Democrat member for Cambridge, who pointed out that mitochondria were once free-living bacteria, which, in the dim and distant primordial era of life, had set up home in other free-living microbes - eventually evolving into people, including the assembled members.

This is why the DNA of the mitochondria have a completely different origin from the DNA of the human chromosomes, Mr Huppert said, a statement which somewhat flummoxed the rest of the House.

Just as things were in danger of getting a bit technical, Fiona Bruce, the Conservative member for Congleton (not the same Fiona Bruce who reads out the BBC news), came up with a bit of touchy-feely philosophy.

"Once in a day I was an embryo," she said wistfully, adding with sterner emphasis "and so was every member of this chamber." The statement of the blindly obvious seemed to generate much hilarity among the fully grown-up embryos on the other side of the chamber.

But things soon settled down again into the thorny issue of medical ethics and scientific terminology. Steven Baker, the Tory member for Wycombe and a former RAF engineer, decided to drop a few heavyweight names: Karl Popper and Thomas Khun to name two.

He said that there was a lot of "semantic sophistry" over whether mitochondrial transfer was genetic modification or not. If the germ-line is to be modified, Mr Baker said, then it is indeed genetic modification, and he for one was having none of it.

Case study: The Vlachos family

Julie Vlachos, 47, from Worcestershire, has two children, Alexandros, 14 and Aliki, 12, who are both living with mitochondrial disease. She lost a daughter at birth to the same condition.

My children have a mitochondrial disease called Leigh's disease. Sadly we didn't know until after we'd had all three children - by which time of course it was too late to do anything.

Aliki was taken extremely poorly at 15 months old and only then did we get a diagnosis. We found out that's why Maria, our first daughter, died, that's what was happening with both the children. Then we found out I had this condition. Aliki doesn't have any speech, she doesn't walk. Most of her organs are affected so she has multiple medical needs.

Alexandros is in a wheelchair most of the time and has heart, sight, muscle and renal issues. It's a very cruel and painful disease that affects different children in different ways. For me, having a baby with DNA from another woman isn't an option.

Sadly, because I'm 47, I'm out of the picture. When a woman gets to my age, the chances of having successful IVF anyway is very low. For younger families in our situation, it's going to make a massive, massive difference. We can stop children suffering, and it means that families like ourselves can have healthy children that are their own."