Car insurance for young driver

[AsterixInEngland]

I have been looking at adding dc to my car insurance but they are refusing to insure someone under 20yo.
I found Marmalade that would cover ds for occasional use of my car. Is there any other insurance like that? Or is that the only/best one anyway?

I used Direct Line 1st year (had a black box) and Admiral this year. This is as him being a student non main driver.