It's about building control, not planning.

No. Planning.

Generally speaking, planning rules are not affected whether it is a
conservatory or an extension, particularly in reference to exemptions and
permitted development etc. The fact that it is a conservatory only become
involved if there is an element of appearance in the mix, such as attempting
to maintain the appearance of a conservation area, or your front elevation
facing a highway.

The conservatory is being changed into an extension. Inside of a part time
room (conservatories are for plants) it become a full time room.

Well, the term conservatory has a special meaning under planning and
building law and it has nothing to do with plants, whatever the Victorian
definition of the word was.

It can still be separate from the rest of the house with external grade
walls, doors and windows. A reason for the tiles could aesthetics, and no
rain noise.

Yes, but it is not allowed under the building regulations without some
serious hoop jumping. Basically, to enable you to have glass walls, you NEED
the conservatory building control exemption to apply. For it to apply, you
need a translucent roof.

You can get a glass walled non-conservatory to pass, but it is a serious
business, probably involving superinsulating the rest of the house in
compensation.

Christian.