I think most sub-lingual use of anything ends up being mostly oral, even with pills, given the amount of filler relative to active content. But I've never heard of sub-lingual use of H, and given both the low quality of most UK gear and the terrible oral BA, suspect it would be a waste.
I've only used a few times since a period of chipping in my youth - back when I think most London stuff was Iranian or Pakistani, maybe even SouthEast Asian. That snorted and smoked pretty well, though I never really got the hang of chasing the dragon. I only really bother with pharms now, but back in '05, snorted street powder - it was definitely a LOT less effective than smoking, and white shit came out of my nose, like Uma Thurman in 'Pulp Fiction.' Last year, in the kind of company who don't take 'no' for an answer, I used for a few days - street bags, .2's, which the crowd I was with smoked in rock-style pipes. I didn't find that very effective (thought you never applied a naked flame to opiates?), and snorting the stuff - which was solid brown, almost looked like US tar but lighter - was both a hassle and produced very little effect. Like .1 with a modest tolerance from CWE's and occasional DHC insufflated had about as much of an effect as 100mgs codeine, if that.
I saw one girl mix up a shot, and she had to use citric acid - which I thought meant the gear wasn't water soluble, or had low solubility, and thus can't really be insufflated? But generally everyone seems to either chase or use needles. I don't think UK gear is meant for snorting, let alone sub-lingual.
Quality's dropped so far I won't bother again in this country - pharms are easy enough to get hold of and more reliable. But your best best is probably chasing - just start small, as it'll hit harder and faster than insufflating, and scroogle for a guide to chasing technique - I could never get the running part right, and either ended up smoking the cut, which could make for bad headaches, or burnt up most of the diamorph. I certainly wouldn't put the shit that goes around in London in my veins.
As to medical diamorph being used intranasally, it's a completely different product from street shit, so I don't think that study has much relevance to non-pharm gear. From what I've read, even oral use can be quite effective if you're dealing with pure pharms: but the one time I was offered 30mg tabs, I decided against - I'm bad enough with the milder opis, a pharm-grade tolerance and habit I don't need.
