These are nervous times at the opera. When should we expect the gratuitous rape scene? Will the director relocate the action to a Croydon laundrette? Who might be booed, and for how long? With Opera Holland Park’s Lakmé, however, almost any of these diversions might actually be welcome — anything to save us from the tasteful visual torpor that looms over Aylin Bozok’s production like a choking black cloud.