As much as appreciate the advice I was given it was incorrect as far as I am concerned. I put the Marinara sauce into the blender, blended it for a while, then added some veg stock and continued to blend, then added to a pan and put in some double cream, it tasted great.

In jail ma'am. Down by law.

I should've added a "JK" to my answer. Hey, where did you learn the prison technique?

Could we define "decent"? My answer is no. It might improve the sauce but it won't be a real soup. A soup needs to be "looser" than marinara. Of course you could try the prison technique of adding hot water to ketchup. Either way it's not going to be good.

Sure it will.