Home Office figures show 37 people attended citizenship ceremonies in the area in 2020 – 27 fewer than the 64 the year before.
Since the figures were first published in 2004, 1,077 people have gained citizenship in the area.
Just under 75,000 people took part in citizenship ceremonies nationally last year – a drop of 34% from 2019, and the lowest annual figure since 2004.
The events are the final step in the process to full citizenship and being able to obtain a British passport, but were suspended for large parts of 2020 due to Covid-19.
Participants are asked to make an oath of allegiance to the Queen and pledge to respect the rights, freedoms and laws of the UK.
Steve Ballinger, director of communications at the think tank British Future, said: “Registrars worked hard but Covid meant many ceremonies were delayed – and people don’t get their papers until they have attended the ceremony.”
The Institute for Public Policy Research think tank wants the current process reformed.
Marley Morris, IPPR associate director for migration, trade and communities, said: "For many, citizenship ceremonies are an important symbolic moment, yet they have a low public profile.
"Councils should explore ways to celebrate citizenship ceremonies more widely in their local communities."
A Home Office spokesman said: “We continue to work closely with local authorities to ensure anyone who requires a British citizenship ceremony can attend one as quickly as possible."