From an MoD response to a Freedom of Information request in 2012. Has their thinking changed in the meantime?
https://www.whatdotheyknow.com/request/review_of_world_war_ii_service_r"The agreed policy between MOD and The National Archives is that service
records will be transferred to The National Archives at the point that the
majority of the subjects of the record have passed their 100th birthday
as, until that point, the record relating to any one subject will be
closed. Whilst MOD and The National Archives have not discussed in detail
the transfer of Second World War service records it seems likely that the
records will become publicly available in the mid-2020s given that an 18
year who enlisted at the mid-point in the war would have been born around
1924."
