Replacing old flooring - remove or cover?

[madkingsoup]

I have an old Victorian kitchen which I am updating. I was planning on taking the floor down to the ceramic tiles (in the original bathroom area on one side) and floorboards (on the main part of the kitchen) in order to then level it off with a levelling compounds and then as I see fit.

The floorboards side of the kitchen is quite uneven and so I started to remove the layers of old vinyl tiles. I have now found the horrible bitumen-like substance mentioned elsewhere and so there is obviously a long and arduous task of removing it.

So, should I continue to go down to the boards, seal the nasty adhesive and then level it all over? Or should I simply go over the top of it?

Basically, am I bodging the job by covering it all over?

Thanks for any help or suggestions
Nealix