Can I paint kitchen tiles with Matt wall paint?

Yes. Make sure to clean them thoroughly first. Kitchens are notoriously greasy places and any grease on the tiles will stop the paint from adhering.

It might be no harm if you can run a sander over the tiles first, as this will improve the 'purchase' of the paint if the tiles are particularly well glazed. If you intend the paint to adhere and be washable you must put a good primer under it, a light sanding of the tiles, followed by wiping it down with a tack-cloth (to remove all of the dust) then use a a primer such as Kilz (not Kilz 2 it is latex and does not work near as well). Once the primer is dry you can top coat with anything.