The boss of the new, enlarged ambulance service serving Wiltshire believes it will lead to improved performance for patients.

Great Western Ambulance Service (GWAS) merged with South Western Ambulance Service Foundation Trust on Friday.

The new ambulance service, called South Western, will serve a resident population of more than 5.3 million plus an estimated annual influx of 17.5 million tourists.

It covers Wiltshire, Avon, Gloucestershire, Somerset, Dorset, Devon, Cornwall and the Isles of Scilly. The head office is in Exeter and the merger took 14 months to conclude.

Ken Wenman, chief executive of South Western, said: “Since South Western has been working with GWAS we have moved from GWAS being one of the poorest-performing ambulance trusts to last week being the best in the country on response times for life-threatening calls. We have spent a lot of time looking at how we deploy our ambulance resources and sending the right resources to incidents.”

The service employs about 4,000 people and Mr Wenman said all staff from GWAS had transferred under their same terms and conditions.

He said the jobs of clinical frontline staff were protected but about 20 posts would be lost in administration and management. Consultation with affected staff has started and will take five months.

Jenner House, on Langley Industrial Estate, Chippenham, which is the headquarters of GWAS, will close in December and staff will relocate to other offices.

He said there were no plans to close ambulance stations and in fact a new ambulance station will be built to replace the one at Malmesbury Road, Chippenham.

Mr Wenman said the benefits of merging the two ambulance services included economies of scale to obtain better value in buying medical equipment and ambulances. As a foundation trust, South Western will be able to use surplus money to reinvest in services.

The new ambulance service will have to make savings ordered by the Department of Health of £10m a year.

The Wiltshire emergency control room at Wiltshire Police’s headquarters in Devizes will close in March, saving £700,000 a year, and 999 calls will be answered at its control room at Bristol.

Although the GWAS name will disappear, Mr Wenman said the only replacement signage will be at the 34 ambulance stations in the GWAS area, which will cost £4,500.

He said changing the name on ambulances and other things would not take place for several years as the total cost of this would be £260,000.

Jo Fowles, secretary of the GWAS branch of Unison, said the union cautiously supported the merger.

She said the change was unlikely to affect the service to the public but many staff would be worried that their jobs were at risk.