Hi MSE1828
You say that the kitchen lighting circuit trips, but does half of the house circuits trip at the same time?
If not, are we talking about a 17th Edition Split Board with 2 x RCDs, or RCBOs, one of which protects the downstairs lighting only?
I believe it would be a good idea to post a photo of the board on the Forum, with the lid off, assuming you know someone qualified to take the lid off.
It also presumes Forum rules allow you to post the photo.
With regard to redress, I would ask the builder if he can supply the Certificate for the work, or failing that, obtain the electrician's details from the builder.
If these tactics don't work, then suggest that because the installation is not working properly and apparently not tested, it may be dangerous and illegal and you will therefore approach your local Building Control, for further advice. That should trigger some action.
However, if you feel you just want to cut your losses and get the problem sorted professionally, then, as already suggested let one of the local Forum Members resolve the problem for you. Good Luck!!
SBS Dave