Highlights - Thomas pips Twell in 1500m
World junior 1500m champion Stephanie Twell will run for Scotland but is undecided on competing at next year's Commonwealth Games in Delhi.
The Colchester-born 19-year-old qualifies through her Scottish mother Isobel, who is from Paisley.
Twell, a three-time European junior cross country champion, set a best time of 4.03.62 seconds when winning in Warsaw last month.
She was second at the UK Championships in 4.09.55 at the weekend.
"This is something that we have considered for a year or two and I knew in my heart that I would always opt for Scotland," said Twell, who raced in last year's Olympics, finishing sixth in the opening heat.
"The time is right for that and my family - in particular my mother, who is from Paisley - are pleased with my decision.
"Edinburgh has been a great place for me to race. At the televised cross country event in January I have always had great support because I think everybody knows I have Scottish roots.
"I am really looking forward to attending the Bank of Scotland squad night with my coach Mick and Liz McColgan next month and racing over 800m in Grangemouth.
"I would love to compete in Glasgow in 2014 in a Scottish vest. That's going to be an amazing experience, but right now I am just concentrating on getting the best out of myself this summer.
"The women's 1500m has suddenly become an exciting event in Britain and the competition is extremely hot. I need to work on improving with every race."
Twell's coach Mick Woods said that he had not yet decided whether she should travel to India with the Scottish team in 2010.