It is normal, they do not seem to call everyone down for the interview even if they're coming to London.
I applied in April'10, they came to Singapore in April'11, some were called, some weren't called. I was the one left out. Emailed them, but you get the standard reply.
Please be advised that your application is still on our list of applications to be processed. Your application will be screened and considered along with all other eligible applicants in your geographic area when we next select for any future interviews.