Plans to close custody cells in Taunton and open a new centre in Bridgwater have been defended by the police.
Concerns have been raised that it would mean officers would waste time driving arrested people 11 miles (17km) to the new centre instead of being on patrol.
Under the new plans rather than doing the paperwork themselves, officers will be able to drop arrested people off.
Avon and Somerset Police said the new building would make the booking-in process more efficient.
Ch Insp Mark Evans, who is in charge of the project, said officers currently spent on average seven hours with each detainee.
'Times of austerity'
The building is part of an £80m project funded by private finance initiatives.
It also includes new custody centres in Keynsham and Bristol.
The plans would mean those arrested will have to be driven to magistrates' courts in Taunton or Weston-super-Mare as the court in Bridgwater is closing.
Ed Boyce, a criminal law solicitor in Taunton, said: "I'm far from convinced that it's a priority or necessary in these times of austerity.
"It's rather difficult to see because if police arrest somebody in Wiveliscombe or Taunton or mid Somerset, instead of driving to Taunton, they are now going to have to drive them back to Bridgwater.
"I can't see how that is going to save time and even if it is a saving of time, it's going to have to be a considerable amount to make it worth £80m."
But Ch Insp Evans said: "Yes this is a large amount of money that we're spending on a new building but it is essential to build these new sites to make sure we can achieve the change we need to deliver policing to our communities.
"Our existing facilities don't provide us with sufficient custody provisions in the right locations."