Not sure how useful this one is. I was looking for stats on ILR applications: "This briefing gives details about how many non-European migrants are grantedsettlement in the UK every year, their demographic characteristics and the various bases for their grants of settlement." http://www.migrationobservatory.ox.ac.uk/briefings/settlement-uk
"The vast majority of people granted settlement for family reasons are spouses and children: 99% in 2014. The majority of migrants granted settlement as spouses are married to or partners of British citizens, as opposed to settled or settling migrants. As Figure 5 shows, in 2013 about 86% of migrant spouses granted settlement had a British spouse or partner, while about 8% had a spouse who was settled or settling in the UK but not a British citizen. The remaining 6% were classified in categories for which the citizenship of their spouse was not specified, such as 'common law spouse' or 'granted settlement on arrival' (see Home Office Immigration Statistics tables for more detail). These proportions have remained largely similar since 2006 when the dataset began."
