According to this article M&S reached 500k in its first 7 weeks on sale, so it must have been close to 600k at the end of February.
http://www.charttrack.co.uk/?i=523&s=1111
So it probably was at the high end of the range at the end of April and adding May's numbers to the total will get it close to 900k now. Selling 100k in the next 2 months certainly seems plausible to me, so if it doesn't get to diamond in July it should definitely blow past it in August (with the additional support from the real Olympics)