Clever way to create access panel in this kitchen unit?

How handy you are and what tools you have at disposal? Do you have router? If so you could:

1.Introduce additional support to keep cabinet shape at the back bottom - heavy-duty angle brackets affixed to the wall and cabinet, providing cabinet R side is right against the wall - screws to the stud/block-work(yellow), you want v-good support on the both sides as your sink seem heavy.
Front L leg seem to far from the edge that it should support(does that bottom bowing under wight or its picture at the angle distortion?) - see if can be moved to the left as close under cabinet left wall for better support.

2.Pre-drill pilot holes for router-bit to go in(just to the depth of panel thickness+0.1mm) and trim-out red outlined sections(pat-saw the bits at the corners that router cant get), keeping 4-5 inch of the bottom panel to allow cabinet legs to stay as they are(loosing one leg far right, unclear if there is one at all…).

3.To cover up, you will require new bottom and some side panel(navy). Few screws to the original bottom(whats left of it) and perhaps some support at the far R corner.

See if this would work for you

BTW: what is this?!?

I’m not a Plumber but I can’t imagine that the soil pipe was ever going to work

to many bends and not enough of a slope

Unscrew the two screws and see whats behind it. If there are terminated wires test to be sure there not live.

I should add them cracking the sink and telling you to buy a new one is the icing on the cake.

I've no idea either, running the soil pipe straight over and then connecting the others to it is what should have been done.

Doubt there should have been any need to move the sink and dishwasher then. This should be on the WTF plumbing thread.

Right there is where the soil pipe from the toilet should have gone directly. The 40ml pipe should have been connected to the soil pipe exactly where you see it!

The mind boggles.

The search function is not working properly here but even with what is available it shows him asking what seems like basic enough plumbing questions as recent as March of this year.

This thread is in DIY - my bad that i assumed you intend to Do It Yourself 😉

Now that i spend half an hour reading your original thread and looking at images - no point destructing fine cabinet - it has suffered enough already.

Looks like to rectify that problem you will have to remove sink,cabinet and have proper access to pipes, not just "hatch door".

Of course without exact measurements hard to say for sure, but wouldn't it be better:
instead gaining ~4" to have toilet outlet right to the back, have it from left side. You would need to box it, but you would loose many bends, shorten the length of 4" to the main stack and gain some fall

This perhaps would affect what design toiled could be installed, but you would have shelve for your rolls and brush 😊
90 bend would need to be replaced to one with 50mm inlet to allow shower connection, something like this

Fall levels to be ensured

Perhaps, but not necessary. Even your current-one might just work.
As said - you need to get plumber(different one)or someone with "knowledge and imagination" to asses current installation, measure and confirm this version of pipe layout would work/fit.
Due to boxing for the pipe your toilet might need to be moved forward - clearance to entrance/door to be checked. In some situations(as potentially yours) compromise might be taken in consideration(toilet protrude into door opening by few inches).
Main thing remain - pipe fall levels to be maintained to ensure waste water escape in acceptable phase to prevent backing-up to any/all appliances.

I think that the blockage is from a lack of fall, but yes, a good plumber would be the best bet there now that you've opened up the access.