RBS school for example manages to get 100% employment for its graduates but these jobs are rarely permanent. Most companies give temporary contracts for up to a year so even getting into the big two ie RB and RBS doesnt mean the dancer is there for ever as they have a kind of probationary year. If you look at a list of RBS graduates a year later a huge majority will be somewhere else...... not just the UK students, but the overseas students will have moved about too, as often european companies take students from schools as apprentices and then only keep one or two when the apprenticeship ends after one year. They then take another batch.
Northern ballet school as far as I know is in Manchester and Northern Ballet is based in Leeds. Northern Ballet have their own academy which trains youngsters but this does not specifically feed into the company. They use youngsters from the academy when they are in leeds and need children ie for nutcracker. Their home grown dancers come from RBS, ENBS ,Central and Elmhurst and they also take a fair few foreign dancers. There was historically a link with central so several of the older dancers went there but in more recent years the net has been cast wider and dancers come from all over. As far as I know if you are what they are looking for they take you. If they dont find what they want ,they dont just take because you went to school A or school B but wait to see who they see next. This goes for most companies these days I should think because the size of many companies is shrinking because of funding cuts, not just in Britain, as I know dutch National suffered heavy funding cuts last year.