Normally when you want to hide an extractor you purchase a built in one - it fits behind a unit specially built with a door attached. Like this one:- I would suggest you contact whomever you purchased the kitchen from and order the right unit with an built in extractor and return the other one, which is not supposed to fit in a cupboard.

I would suggest looking at Elica - Sleek which fits nicely within a kitchen unit its dimensions are 290mm external and 260mm internally. This can be vented or recirculated Please let us know if we can help in any other capacity

When replacing an existing kitchen in UK, the current recommendation is that you replace your old extractor with one that’s as good as or better than the previous one . If it’s above the hob it needs to remove a minimum of 30 litres per second if it’s elsewhere in the room it’s a minimum of 60litres per second . There are advantages of having a higher extraction rate than these - ie less moisture in the air - less sticky residue on door fronts and shelves etc! The m3/ph is just another form showing what it does/how efficient etc and can be useful if you want to work out the volume of the room and the air you want to remove etc . Hope that helps ?! It’s basically what your builder suggested - he’s obvs got your back ! Nice to have one on board who’s not trying to help you overspend !!

Thanks all, this problem has now been sorted. We are having a flush ceiling mounted extractor whcih fits neatly beteen the beams. This will be in the centre of the kitchen ceiling (rather than 'almost' above the hob to one side of steel beam). It has an extraction rate suitable for use away from hob so ticks the box for building regs. The ducting can run along the joist, through the bricks above the steel beam and then will be boxed in along the beam to the external wall. This beam is already being boxed out to accomodate the soil pipe from upstairs running the other direction. This way I get to keep my island free from hanging extractor, pop up extractor and get to keep the full drawers below hob. We are so relieved to have finally settled on the right solution for us. Thansk again for all the input and advice.