Conks - you aren't going to be able to fit these lights, not legally anyway.
The work is notifiable (see
//www.diynot.com/wiki/electrics:part-p), and since it is notifiable, there's no way you're going to be able to get Building Regulations contraventions past the BCO. It isn't just Part P that you have to comply with, it's all of the relevant regulations, and Parts C & L are immediately obvious hurdles.
As you have a roof over the kitchen then you will have to completely seal around the lights as you must prevent warm moist air from entering the unconditioned space because if you don't you'll get condensation up there - a contravention of Part C.
But you can't completely seal around the lights as you have no access from above.
Part L problems are twofold - you may not remove it the insulation around the lights because if you do that will make the degree of insulation worse than it was before, i.e. your degree of compliance with Part L will be less satisfactory than it was before. But you can't leave the insulation in place because the lights will require a clearance all around them to avoid overheating, so you'll need to install some kind of structure around the lights to provide clearance and to allow the insulation to be maintained.
And you can't build a structure around the lights as described
here, for example, or use a pre-formed cap such as
this because you don't have access or the vertical space needed.
The second Part L issue will be the efficiency of the lights. Assuming that your intention is to use small recessed ones, these will not be efficient enough - even though the Building Regulations don't actually mandate luminaires which cannot take incandescent lamps that is what Approved Document L says you have to use for a certain percentage of your lights, and rightly or wrongly many councils regard that as mandatory, so you could have a real struggle to get MR16 sized halogens passed.
