A "retail revolution" is needed to help people choose health options, a food watchdog has said.

Food Standards Scotland (FSS) commissioned a report which calls for "radical steps" on the way food is displayed and promoted.

FSS said Scottish obesity levels, currently 30%, are projected to rise to 40% by 2030.

The report, which was prepared by the University of Stirling, also backs the idea of a sugar tax.

But the Scottish Grocers' Federation (SGF) said the report failed to take account of the efforts already being made to promote healthy eating.

FSS senior dietary adviser Dr Gillian Purdon said: "The report supports Food Standards Scotland views and recommendations for the need to extend sugar tax beyond soft drinks, to reformulate products to reduce sugar fat and salt, to resize portions, address less healthy food promotion and to provide clearer consumer information on products in both the retail and out of home sectors.

"This report will help us to develop new approaches to improve the balance of food offered and promoted by the retail sector.

"It is clear that a combination of measures will be needed overall to enable healthier eating. Regulation of promotions of high fat, salt and/or sugar food and drink within retail stores and out of home premises should be taken forward as a priority."

Previous research by FSS indicated about 50% of less healthy food choices are purchased on promotions. For healthier foods, the figure is about 30%.

The report added: "We conclude that the current context for consumer choice in-store is affecting the health and diet of consumers in Scotland.

"Voluntary and self-regulatory approaches or relying on consumers to make 'good' decisions are not having sufficient impact.

"It will thus be necessary to regulate to make the changes have real impact."

SGF, which represents food retailers in Scotland, has criticised the report.

Its head of policy and public affairs Dr John Lee said: "This report seems to ignore the significant efforts of retailers to actively promote healthy products in-store and the efforts of manufacturers to reformulate products and reduce calories.

"Additionally, extending the sugar tax will make no real or lasting impact on diet-related problems. Improved food education and awareness should be the priority rather than constantly shifting the responsibility for population health onto retailers.

SGF said its Scottish government-supported Healthy Living Programme currently had over 2,000 stores participating.