Ergotron 33-350-200 WorkFit-S with-Adjustable Workstation.

Retails for £520 - https://www.jp-uk.co.uk/ergonomic-mounts-workstations/workstations/height-adjustable-workstations/ergotron-33-350-200-workfit-s-single-worksurface-workstation.html

Happy to accept £250 ONO

Convert any surface into an adjustable-height standing desk with the attachment of the WorkFit-S. Make computing comfortable for prolonged periods—stand up whenever you want. This sit-stand workstation is extraordinarily simple to use. With the push or pull of a hand, you can instantly raise or lower your keyboard and display in one easy motion, yet all the while the system will remain stable throughout your work routine.

Specifications of the Ergotron 33-350-200:

Colour: Black

Typical LCD Screen Size: ≤ 24"

Weight Capacity: 2.3 - 7.3 kg

Lift: LCD and keyboard adjust 18" (46 cm) in tandem; LCD adjusts 4.8" (12.2 cm) independently; maximum LCD height adjustment = 22.8" (58 cm).

Tilt: 30°

Rotation: 360°

Mounting Standards: VESA FDMI MIS-D, 100/75, C (hole pattern: 100 x 100 mm & 75 x 75 mm)

Worksurface Dimensions: 6 x 585 x 380 mm

Keyboard Tray Dimensions: 6 x 685 x 226 mm