Since the OP is from England (at least based on his username I assume so), I want to mention that those from the U.S. that said that your former name will appear on the report may be incorrect for his case. IIRC I think under the UK's Gender Recognition Act the agencies are required to remove a former name changed due to a gender transition. On legal issues where one lives can make a big difference (so remember to keep that in mind, especially when there are clues as to where they live*). As I say, the physical aspects of transition vary more by the direction of transition (FTM vs. MTF) than where you live, while legal issues are the opposite.
(As a side note, as anyone who has moved to a foreign country or has hung out on an expat forum can tell you, for better or for worse credit history does NOT generally transfer internationally; the credit rating systems are often completely different. Since a U.S. credit report's names are based on ones you've used to obtain credit, moving there for the first time after transitioning would be an exception to your former name appearing; likewise for someone whose name was changed for whatever reason before being old enough to have a line of credit. Conversely if you've used a variant of your name, such as your middle name or nickname as the given name, to obtain credit that name will also show up.)
*A cue I've also used in the past is if I see a date like 18/8/2013 (the date I'm making this post) that indicates they're probably not from the U.S. since there are not more than 12 months in a year (conversely a date like 8/18/2013 would indicate they are). Also look for spellings with the presence or absence of extra u's in words, etc.