Automobile glass is very efective at blocking UVB, the radiation that causes sunburn. It is less effective on blocking UVA, which can cause skin cancer. The front windshield is laminated glass, and the lamination effectively blocks both UVA and UVB. The side windows are usually not laminated, so they allow more UVA rays. Either a factory tint or an aftermarket tint can further reduce UVA and UVB.
I'm not sure if the MINI sunroof is laminated glass. If it is, it will block both UVA and UVB rays. The sunroof also has a factory tint, which would also block UVA / UVB to some extent. The fabric shade also blocks some UVA/UVB.
My guess is that very little UVA and UVB are getting through the sunroof and shade, but the only way to verify that would be to have the sunroof glass tested in a laboratory, unless MINI has a specification they've released on the UVA/UVB transmittance, which I doubt.
There are both clear and tinted aftermarket films that can be added to the sunroof to block 100% of UVA/UVB, if someone wants 100% protection.

WOW - good catch. Thanks.

I got mine tinted with limo tint on the sunroof and it works great. You can see out but I never notice the sun now. Plus it looks mysterious?

'08 Pure Silver

Ignorance is bliss as the screen doesnt matter as UV rays are absorbed by 99% of automotive glass.

No, read the specs. Auto glass stops 100% of UVB rays, but only about 35% of UVA.

All mini glass (as with most of todays higher end cars) has a factory tint (greenhouse tint is what its called) and protects 100% of both UVA and UVB.

Do you have a source for that UVA/UVB rating?