Conservatory PT3: Inspection Cover questions

Currently having some issues with our DG firm over a conservatory. The plastering is still ongoing and the floor seems to of come to a stalemate for now, next problem.

We had an inspection cover in the garden which is now inside the conservatory. The drain is shared and goes along the back of our terrace houses. The drains are roughly 3 feet deep and from memory the cover was probably 24"x18" maybe a bit bigger. Its no longer here so can't check.

The new concrete floor has raised the cover about another foot and they replaced the cover with a smaller one.

The new one is 300x300mm square plastic, it screws down but is only a single seal. They have also nicked a couple of our marble patio slabs to sit the new cover on which cut across both sides of the hole. So looking down it you now only have a 150x300 slot to look through. The DPM also seems to run through it so its currently like a drum and you can't see into the chamber.

A mate reckons this could be a big problem and says the cover should be larger due to the depth of the drain, and the fact its only single seal.

Is he right? I'm not sure whats compulsory or just recommended. I'd of thought it should be double seal at least

doble seal, screw-down i.c. covers are fairly typical on internal installations.

as this is a connie and not under b'regs then you will have to regulate it yourself.

choking down the aperture like they have is not good and limits your access to the drain channel should you wish to rod the drains.

they should have used a proprietary 600mm x 450mm recessed screw down double seal i.c.cover like this.