LONDON: A full 94% of the top advertisers in the UK now have websites optimised for the mobile consumer, although the ones with separate mobile sites deliver a better experience, according to new research.

The Mobile User Experience Audit from the Internet Advertising Bureau (IAB) UK looked at the user experience of the mobile sites of the top 50 advertisers by media spend in the UK.

Based on seven key measurements, the report revealed that 46% have a responsive design website across desktop and other devices while 48% have a separate version specifically optimised for mobile.

With the assessment criteria covering design features such as site load speeds, easy viewability and concise menus, the audit found the separate mobile websites scored more highly in five out of the seven mobile measurements.

Mike Reynolds, the IAB's mobile manager, said this finding meant advertisers should think differently about the content they serve on mobile devices.

"It's great to see that 94% of the top advertisers in the UK have an optimised site which reflects where people are choosing to spend their connected time," he said.

"It was interesting to see that separate mobile sites scored higher against the user experience measures we looked at," he continued.

"This highlights the need for those advertisers approaching mobile with responsive web design to think differently about the content they serve on mobile devices, and pull in the unique functionality that makes mobile such an engaging device."

Nine out of 10 of the top advertisers were retailers, according to the report, which named Liverpool-based as the top performer with mobile accounting for 59% of total online sales. is part of the Shop Direct Group, whose head of user experience, Sam Barton, attributed its success to experimentation and moving its design and development teams in-house to foster creativity and innovation.

"Experiments enable us to make quick and nimble changes to our websites, removing assumptions, to learn which ideas improve key metrics and should be iterated upon, and which ideas need to fail fast," he said.

Data sourced from IAB UK; additional content by Warc staff