Morgan started his career at Dursley RFC in Gloucestershire before joining Merythr Tydfil and then Scarlets in 2009, and he admitted the decision was far from an easy one.
"I feel privileged and honoured that both Wales and England have been following me and it has taken me a while to come to this decision," said Morgan, who has helped Scarlets into sixth place in the RaboDirect PRO12 table.
"But I'm English, I grew up supporting England and as a youngster I always dreamt of playing for England. Ultimately, if given the opportunity I want to try and take things forward.
"I am thoroughly enjoying my rugby in West Wales and the opportunities, development and experience I've been handed over the past two seasons by the Scarlets is something I am very grateful for.
"I'm eternally grateful to Scarlets because I wouldn't even be talking about this if it hadn't been for them giving me a chance.
"I joined them three seasons ago, initially trying to improve my shape and fitness thanks to the conditioning staff of Brad Harrington and Ryan Campbell, who have worked tirelessly for the first two years to get me into a position where I can get on the field.
"Nigel Davies is a great coach and has been really honest with me and having Simon Easterby, Mark Jones and Vernon Cooper in the coaching set up so fresh from playing is great as they bring a real energy to things. I want to carry on doing the best I can for Scarlets and anything beyond that will hopefully follow."
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