The 2 cabinets underneath are purchased bedside cabinets.
I am not sure of the best sheet material for the desk, ideally no thicker than 20mm, it goes into the corner of 2 walls and a wall to the left so can be supported at the back and also could be supported over the cabinets with steel legs but there will be a 730mm span in the middle front with no support.
The cabinets are laminated very dark maple so this would need to match so I can not find answers on the strongest material, plywood, chipboard or MDT and will it sag?
There is also a pull out keyboard stand below to match.
The problem you will have is obtaining a sheet of material big enough for the top - assuming you do not want joins. 2440x1220 is the largest for many sheets although you can get ply in a larger size.
Yes I did notice this yesterday and reducing it in length from 1250 to 1220 will be ok so I can use a whole sheet.
I was thinking that I would use this hardwood ply from B&Q and laminate it:
From what I have seen on websites this is much stronger than chipboard and mdf so will be able to handle the span better, do you know if this is correct?
stoneyboy is right, the biggest problem you will have with plywood is getting a decent finish on the edges.
personally i'd use MDF, available in 10ft (3050mm) length sheets and you can buy laminated sheets. all you'd need to do is apply iron-on edging. be careful how you cut it though - face down with a circular saw to avoid chipping the laminate.
Have you considered quartz, its available in 20 and 40mm in lots of colours has 7 times the flexural strength of stone and smooth edges. Not sure where you are located but henderstone.co.uk have lots of off cuts available at sensible prices. If you are not in Kent try and ask a local stone yard for a cheap of cut.