They classify 3k as "deepstack"? I"d say that"s about an average amount. 5k and over I would say is a deepstack.
The number of chips you start with is only part of the equation of how "deepstack" a tournament is.
The 30 minute blind levels make the tournament "deeper" than most other £20 freezeouts available in the UK. You could start with twice as many chips, but if the blinds are only 15 minutes that makes it a much less "deep".
Any deeper than 3,000 chips and 30 minute blinds, and the tournament would go on for too long. There"s no way round it really.