Bombardier is a Canadian Company with its headquarters in Berlin. They were part of a rival consortium which included, Siemens of Germany, so presumably work would have gone abroad if their bid had have been successful,
We haven't built any trains on this scale since the introduction of the InterCity fleet in the 1970s, which this contract is set to replace, We no longer have the skills to undertake such a large project on our own. Just like we build cars and planes in conjunction with other countries, the same is true of trains.
The Hitachi trains are proven. They currently operate on the High Speed link from St, Pancras to the Channel Tunnel. Virgin also own some. Hitachi have built a large maintenance facility at Ashford, Kent.
http://www.hitachi.com/New/cnews/071002.html
The bottomline is, these trains are well overdue (no pun intended). The consortium the Government have chosen will be able to deliver a proven train and have it in operation quicker.