Roberts won three individual gold medals and a fourth in the 4x100 metres freestyle relay at Beijing 2008, taking his career total to 11 Paralympic golds.

But when the announcement came, with 16 swimmers' places confirmed and 26 others selected subject to the International Paralympic Committee's final allocation of places, there was no room in either list for the 31-year-old.

Roberts was seeking one gold in London to surpass Baroness Tanni Grey-Thompson's tally and become Britain's most successful Paralympian of the modern era, but he has failed to meet British Swimming's qualification standards after suffering with pneumonia this year. He also suffered a torn triceps in 2009, which placed his career in doubt.

Potential

Atkinson said: "The rationale behind the selections was entirely performance-driven. We only looked at athletes who we considered had medal potential in London.

"Dave, unfortunately, has been plagued by injury and illness, going back to 2009. Because of that he has not been able to demonstrate required results. For example, his best time in the 50m freestyle from January 1, 2011 to the current day would only rank him seventh in the world.

"I talked to Dave this morning just before the (squad) announcement was made.

"He was obviously disappointed but he's looking ahead to what the future holds. We talked about how hard the last four years have been, with injury and illness, and we recognised that has been the issue that has prevented him from swimming as well as he would have hoped to.

"He'll now have a period of some reflection to consider what he does next."

Delighted

Ellie Simmonds, by contrast, will have the opportunity to add to her two gold medals from Beijing. Simmonds won the 100m and 400m freestyle events in the S6 disability class in 2008, aged only 13, and currently holds world titles in those two events in addition to the 50m distance and the 200m individual medley.

She has met the qualifying standard in all four events and, now 17, heads up an initial selection which also includes Sascha Kindred, returning for his fifth Games, and fellow Beijing medallists Matt Walker, Robert Welbourn, Heather Frederikson, Jon Fox and Claire Cashmore.

Cashmore was delighted to be among the group and said: "I feel like I'm in my best shape ever and I'm confident.

"Everyone is going into the event aiming for a gold medal. I went to Beijing aiming for gold but someone beat me on the day, you never know what's going to happen in the Paralympics."

Kindred's wife Nyree - who won 100m backstroke silver in China under her maiden name of Lewis - is among the 26 who have been nominated for further places.

That list features several further Beijing medallists in veteran Jim "the Swim" Anderson, Liz Johnson, Natalie Jones, Sam Hynd - whose brother Oliver is in the initial 16 - Matthew Whorwood, Sean Fraser and Graham Edmunds.

Atkinson continued: "We're very happy with the strength of the squad, we've announced 42 names and there's some great experience in there.

"But we've also got 19 first time Paralympians, so it's a great blend between them and some known performers.

"Of the 42, 11 of them will be aged 18 or under when they swim. The youngest will be Chloe Davies, an S14 backstroke swimmer who'll be 13, but I wouldn't want to tag her, or anyone, as the new Ellie - she's the new Chloe."