Subject Access Requests - Volume and Response Time - Find a freedom of information request

I manage a team in Derbyshire County Council that processes Subject Access Requests, the introduction of GDPR as resulted in a 40% rise in number of request. Currently, we are getting around 450 requests per annum, have four members of staff working full time on these requests and over quarter of requests this year were overdue under statutory timescales before they were released.  We have put in some temporary resources in place to resolve this issue, however need to put long term plan in place,

I am looking for some comparator information to assess our performance before requesting extra permanent resources and wondered if you could give me some idea of the:

1. Number of requests your council is receiving per annum,

2. The number of staff you have dedicated to handling them,

3. How many (if any) were overdue?

1. Number of FOI requests received per annum, for the period 1 September 2018 to 31 August 2019 = 1,496 requests

2. Number of staff handling requests = 1.5 FTE on average

3. How many were overdue = 342