Try Draycott Steep over near Cheddar, that’ll clear out your lungs.
I can definitely vouch for that one, the middle section is evil, ~0.5 miles of ~20%! By luck rather than planning, I managed to cover the slightly extended version in Sept ’20 during our caravan hol in Burnham On Sea https://www.strava.com/segments/9770445
Another nasty climb near Devizes I’ve done is the Kingsettle Hill/Tower Road climb up by King Alfreds Tower https://www.strava.com/segments/2986434 . Small section ~20%, it was quite challenging having just done a VO2 max effort up Gare Hill.
The only climb I’ve done that I reckon is harder than Draycott is Ffordlas/Hillside starting just up the road from Prestatyn train station and heading towards Gwaenysgor. 33% gradient traffic signs might be a bit overhyped, but it’s bloody steep in places, had to meander across the whole road width just to keep moving and not put a foot down on a ~17Kg hybrid after I had mechanical on my road bike.