Personally, I would always go with 1200 or 1400 paper - they do even make a 1700. Not avaliable at B&Q but should be avaliable from a local decor store or trade supplier - or online - 1200 and 1400 do not cost much more.
They provide good cover for inperfections, and being thicker are easier to manage when wet with paste.
These guys supply all grade including 1700 - not sure how easy it would be to use on corners as it is that bit thicker. Never used it myself - just noticed that these guys sold it.
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