Top horizontal surfaces of enclosures do indeed have to be IP4X to meet BS 7671 requirements.
Although if you had to state one overall IP rating for an enclosure, and other bits (e.g. the front) had a lower rating, then you could only claim that it met the lower rating overall - which I might guess could be the case here. It wouldn't make sense to claim an overall IP4X if the front was only IP3X. Obviously it would be better to give the IP ratings for the top and other surfaces separately (Top & sides: IP4X, Front: IP3X) - but marketing often isn't that logical.
Well the requirement is IP4X or IPXXD. The latter would permit a 35mm opening through which a 1mm diameter wire should not make contact with live parts within 100mm.
Strange claim anyway because most boards are complete without any apertures other than screw fixing holes at the rear. I wonder is this a mistake and the claim was meant to be IPX3?
