What is the relationship between the New Kadampa Tradition and Tibetan Buddhism? New Kadampa Tradition is a prominent Buddhist movement in the UK with many centres and meditation classes. However I've always been confused about the relationship between them and Tibetan Buddhist. 

So moving on from this question - what is the relationship between the New Kadampa Tradition and the Tibetan schools? What lineage if any do they claim? Are they a minor school or a subset of another school? I heard somewhere that they had a disagreement with the Dalai Lamaso maybe they are linked with the Gelug school. However that might not be true - all kinds of things get reported about Buddhist organisations that can be classified as new religious movements, some of which are just sticks to beat them with.
The New Kadampa Tradition (or NKT for short) is an offshoot group that broke away from the Gelug school. One of the primary areas of controversy between the NKT and the mainstream Gelug school is the position of a figure called Dorje Shugden, who among the NKT is considered to be Manjushri emanated as a spirit in order to keep the Gelug school pure from teachings from other schools. Among the NKT Dorje Shugden is propitiated as an enlightened being, but within the Gelug school now it is understood that Dorje Shugden is a worldly spirit only, and should not be treated as an enlightened being.

As a result of this split, the NKT is very insular, and will generally only read a selection of books written by their founder, Kelsang Gyatso, and in general are not considered to be part of the Gelug school any more due to Kelsang Gyatso being expelled from his home monastery of Sera Me, but their selection of teachings and practices are all drawn from the Gelug school.