I've been reading the baby name pages with interest and a couple of times someone has suggested the poster should "look outside the top 100 names". Where are you finding extended name-popularity lists? I only seem to be able to find the top 100 for the UK.
The link I posted above goes to a ONS page with search results for baby names - a few lines down (about 4), there's a pair of results called "2011 Baby Names Statistics Boys (Excel sheet 1461Kb)" and "2011 Baby Names Statistics Girls (Excel sheet 762Kb)"
Those are the ones containing rankings for all names given to at least 3 babies.
Cosmo - Are you sure you're on the right ONS site ?
When I googled office for national statistics, the first result was for a very similar looking site called UK National Statistics which just did top 100 lists. It was very confusing.