Foundations - DPM / Flood zone thoughts?

[boxrick]

Hello! I have posted in the introduction forum about this but thought it required its own thoughts. 

Simply put I am renovating and building an extension. I was flooded at the start of the year and my property is raised around 60cm off the ground, we are adding another 10cm approx as part of this renovation.
My foundations are piled with above surface ground beam, with block and beam on top and anti-flood air bricks so the subfloor has ventilation.

The builder has simply thrown down a plastic membrane beneath on top of the soil floor. I don't even know if its taped together. 

From what I read, usual preparation is to basically put down the plastic layer, then sand then compacted hardcore and a thin concrete layer. 

From a flood perspective, I am thinking that a permeable weed membrane and some compacted gravel may be best. 

But right now I basically have a plastic membrane thrown down ( And not installed correctly according to building regs )

Simply put I am looking for some advice on what may be best to do in this instance? My builder I don't believe has built the subfloor up properly, and regardless I don't think thats potentially the right solution given I am in a flood zone. 

What are some peoples thoughts here? 

Edited June 2 by boxrick

[boxrick]

And for clarity a DPM is going *over* the block and beam. 

[Oz07]

Most floors below b&b left bare. @nod had to do concrete and drains on his last house. 

[boxrick]

So basically leaving it bare ( soil ), or a weed barrier + gravel is probably fine from my own pov?