I would imagine evans have worked out their pricing structure based on what it actually costs them to do a job that takes 40 mins as most main dealer/high street retailers do, including store overheads, rent, rates, lighting, heating, wages, staff training, insurance, tools I could go on and on!!
As bassspine has pointed out most smaller LBS stores undercharge on labour and don’t really make any money from it but rely on building up a good relationship with customers, it’s the “Cheep brake bleed today, New bike sale tomorrow!! approach!!