Van Insurance issue - not given permission

Hi, I am really struggling to understand this. I have seen a previous post about a similar issue. I have spoken to my insurer asking if i can use Hiya car, I explained to them several times that the insurance wouldnt be active when someone else is using. Unfortunately, they said that no one allows car sharing (they are a broker). Can anyone recommend a van insurance that does allow car sharing?
Initially my insurnace said I would need hire and reward, and having another insurance would ‘void’ the current one. They then said as mentioned that noone allows. I am very hesistant to go ahead if for some reason there is an issue. So any suggestions or tips would be great . Thank you