Hi thanks for ur input. I went to Apple store yesterday about this issue. The guys in there had not heard of this problem with iPads but only with Macs. Apparently as mac screens are only held on by strong magnets. They can clean mac screens at apple stores but because iPads are "Sealed" they cannot clean them. The guy said the dust must have occurred during manafacture.
As mine is only a couple of months old they of course would replace it no hesitation but my iPad is engraved as it was a given to me as a gift. So they could not give me a new engraved one. The advice was to phone the online customer services and because it's do new there is a scheme whereby they will send an exact iPad Out to you. You put your dusty one in box and return it to them. They will examine the dust/fault. They will either rectify and return or replace, in my case with engraving. When you receive the new iPad then u just return the substitute one they loaned you at the start.
If this all goes to plan I will be very impressed. But I'm still at the stage of deviding if it's worth it. The particle is small only I notice it cos I'm a perfectionist. What I do think though is that could one bit of dust lead to more later in my warranty or even outside it!