Painting Plastic coving

Could try BONDIT PVCu CREAM CLEANER, a very good cleaner, it might restore the cladding.
Astonish UPVC Cream Cleaner is another one which apparantly is good, never used it myself.

http://www.bond-it.co.uk/product/pvcu-cream-cleaner-1l/

 

If it wont clean up then paint it
This stuff is great on plastics, available in matt, gloss, satin

Screwfix don't sell it hence the competitors link

http://www.toolstation.com/shop/p84694?searchstr=bedec

ah ha....just re-read post, thought you were talking about trunking ....dunno why, tired me

Coving then.....like this stuff;

http://www.pvccladding.com/products/interior-coving-cornice-519/

Got this style coving in my house, fitted it myself and painted with same emulsion as on ceiling, nice finish, matt

As yours is in a bathroom, acrylic eggshell would be a good choice as resists steam and moisture penetrating and is wipeable

Give the cove a light sand down (depending on condition its in now and the finish you want to achieve)
Wash down with hot strong sugar soap solution
Wash down with clean water
Fill any cracks, dents, sand down, dust off
2 full coats of acrylic eggshell, following manufacturers instructions / drying times

That coving is gonna look mega in no time at all

If Astra is available, he will give a 'pros' view on the way forward

 

Would not recommend sanding plastic as it will show up all the scratch marks, simply as already mentioned wash it with a sugar soap solution, rinse off and let dry. Personally I would then apply 2 coats of Zinsser Bullseye 123 followed by 2 coats of acrylic eggshell letting dry between each coat. Bullseye is the more flexible of all the Zinsser primers and eggshell the ideal paint for areas of high humidity and steam.

 

When I said I light sand, around P180 will be fine

Don't know if it's been previously painted, may have bits and bobs in the paint but as I said, also depends on what finish the chap wants

Fitted this type to 6 rooms in my house and only came in 2 m lengths so a fair few joins and mitres

Touched up joins and mitres (where needed) with Ronseal 2 part filler and no probs with sanding. Believe me, joints are invisible. Light de-nib between coats (may have primed 1st)

Sure will scratch like *uck with P60 but let's hope the op ain't gonna go that low