Low pay has been blamed for a recruitment shortfall which is causing the south's ambulance service to miss its response targets for 111 calls.
South Central Ambulance Service (SCAS) is required to answer 95% of its calls within one minute.
However, latest figures show just under 66% of 111 calls were answered in 60 seconds in February 2019.
NHS staff said the recruitment of call handlers was a "real challenge".
Berkshire West Clinical Commissioning Group (CCG) nurse director Debbie Simmons said highly-pressured staff could earn more working at the outlet shopping centre Bicester Village, the Local Democracy Reporting Service reports.
"It's a real challenge with regards to the recruitment of the call handlers," Ms Simmons said.
"We had a deep dive into it last time and they're in a position whereby the police call handling centre, which is a few hundred yards away from the ambulance trust call centre in Oxford, has a starting salary [for its call handlers] that's £4,500 more than SCAS.
"The police pay more. Staff can get paid more at Bicester Village and that's a fact. It's a real high-pressured job with real responsibility. It's a real challenge and one where I'm not sure if they know what else they can do really."
Last month's 65.9% figure was down from the 86.7% reached in May 2018, according to SCAS.
The service said in a statement it had experienced "some challenges" in the past nine months with regards to the time it took to respond to non-emergency calls.
It added: "We are also experiencing higher levels of demand for our services, and that, combined with some issues we have had in the recruitment of new staff over the winter months has led to a negative impact on our call answer time."
SCAS added it had continued its recruitment process over the winter and recruited 17 new members into its 111 service since January.