The Home Office publishes data, in its quarterly Immigration Statistics release, on (a) the number of applications in the UK (table as_01_q Asylum, volume 1), and (b) the number of applications that were granted (in the same table), by nationality.
Latest edition available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/758192/asylum1-sep-2018-tables.ods
2018 (to end Sept)
Note that initial decisions are based on date of decision and do not necessarily relate to applications made in the same period. For example, a decision in 2017 may relate to an application made in 2016.