Since you're on 2012, you can use FORMAT
instead:
SELECT FORMAT(GetUtcDate(),'yyyy-MM-dd HH:mm:ss.fffzzz')
Which produced, a short time ago:
2014-05-13 08:23:29.093+01:00
(Or, you could use 'yyyy-MM-dd"T"HH:mm:ss.fffzzz'
if you want the T
separator instead of space)