Online bank First Direct scored 87 for the overall level of customer satisfaction, helping it overtake better-known brands such as Amazon and John Lewis in a ranking compiled by the Institute of Customer Service (ICS),
LoveFilm clinched the title for most improved company, having climbed into fourth place, while Volvo and TSB also showed impressive growth, reaching the top 50 for the first time.
Ovo Energy was the highest new entrant to the index, coming in at 13th place.
However the overall customer satisfaction score in the UK was 76.2, a barely noticeable rise of 0.2 since January, suggesting customer satisfaction has flat-lined over the last six months.
"UK plc must do more to address rising customer expectations. Organisations that ignore consumers will find it difficult to compete with those that already have a long-term culture of customer service. The longer we wait the more difficult it will be to implement," Jo Causon, chief exec of ICS, said.
The data is based on 39,000 responses from more than 10,000 people.