Mr Punter

If it is for surface water, a slot drain can look very neat.

Sorry to hear this but at least you got a definitive answer. I would not go anywhere near a 450mm foul sewer with a high velocity flow.

You will need a SE design for this. If your preferred builder does not like the SE proposal he would need to come up with a counter proposal with reasoning, that can be put to your SE for consideration. You could get a price for both.

CT1 is a favourite on this site.

I think if you unscrew the white waste pipe - which you should be able to do by hand - you may be able to get to the waste from underneath. Failing that, you may need to replace the waste. Is it a clicker one?

Is there anyone around that you can blame?

Be very wary as width, length and depth are often confused. It is errors such as these that can lead to screwups. For kitchens I consider length and width to be side-to-side and depth to be front-to-back. Height and thickness can also cause confusion. With some of the induction hobs in a 600 deep worktop there is often only 50mm remaining front and back after the cutout.

These worktops often arrive with the cut out not fully formed, to give it more strength when moving and fitting.

The cardboard tubes are good for protecting metal profiles. I use a chop saw to cut them up for disposal.

The masking tape sounds sensible. Run round the join with a fugi to remove any excess, then remove tape before it cures.

Truss clips to prevent uplift, noggins to prevent twisting.

It is what I would do, especially in Scotland.

Just go with the original SE design. Send the drawings to Keystone or IG for a take-off and quote for the lintels.

+1 Adjacent cupboard.

Is this stuff just plastic?