1) There is no way that you'll be able to keep the required thickness of insulation if you fit those lights, therefore you will be making the roof less compliant with Part L than it was before, therefore you will be in contravention of the Building Regulations Part L.
2) As it's in a bathroom you must install a
sealed cover over the lights (firehoods and/or fire-rated downlighters will
not do) otherwise you will get warm moist air from the bathroom entering an unconditioned space and condensation will result. That would contravene the Building Regulations. Since the only way you can seal a cover over the hole is from above, and you can't do that now the roof is there, if you install these lights you
will be in contravention of the Building Regulations Part C.
3) Both 1 & 2 will be significant contraventions because lights like that are so bad at lighting a room that you'll have to have lots of them, and unless you have a friendly BCO he may rule that the mere presence of lighting which can take non-energy efficient lamps is in itself a contravention of the Building Regulations Part L.
4) Installing lights in the room is notifiable, so even if the BCO isn't bothered about (3) I very much doubt he would let you go ahead because of (1) and (2).
Basically you cannot have this type of lighting - if you wanted them then you should have planned it much earlier so that you could have built a deeper roof and sealed the holes while you still had access from above.
Whether your wife likes it or not it is now too late.
5) FYI - the
IEC definitions of voltage bands are:
- Extra Low Voltage: AC below 50V and DC below 120V
- Low Voltage: 50 - 1000V AC or 120 - 1500V DC
- Medium voltage: 1kV - 35kV
- High voltage: 35kV - 230kV
- Extra-high voltage: >230kV
This is not some pedantic technical point - if you start getting involved in doing your own electrical work, and start learning about regulations etc you'll come across references to "Low Voltage", and it'll be no good you thinking that that means 12V...