HighlyVolatile

Hi, I'm new to this forum, and I am looking for advice on an issue I am having with floor insulation. I have a suspended timber floor within my living/room dining room, and I am trying to insulate it before I lay vinyl click flooring. I have followed the method outlined by Ecological Building Systems, where I have got under the floorboards and stapled the vapour barrier between each joist. It was going well, until I discovered the remains of an old chimney breast, and I not sure how to proceed. My first issue is trying to reach under the boards. The gap between the bricks and the board is only 100mm and I cannot reach far enough to secure the vapour barrier to the joists. I was trying to avoid the lifting of any floorboards, but I was debating whether to admit defeat and pull them up, but then I have concerns regarding the ventilation. I may have misunderstood, but the guidelines within the gov.uk documents state that the joists must have a gap of 150mm below them. Problem is, even if I do manage to get the boards up and fit the insulation, it will effectively fill the entire space with insulation, and it will have no air flow beneath it due to the bricks. I also wondered whether I could just leave this section of the floor without insulation, but the EBS have warned me that the area could be susceptible to damp. They have also suggested that I remove the top two rows of the bricks, but some of the joists are actually supported by it. As such, I am now a point where I don't know what to do with it. I am also debating on whether to give up altogether and just rip it out, as I have to admit that I don't have much confidence in floor insulation. It just feels like a recipe for rotten joists. Would anyone be able to advise me on the best approach for this? Thank you for your help!