Firstly; in terms of interviews, I would not think about what the Bain London office is specifically strong in. All interviews at Bain are pre-written and taken from a global database (except maybe some partners who are given free reign). Therefore, focusing on specific industries which Bain London is strong in won't be particularly helpful.
That being said, to answer your question, Bain London's key industry strenghts are (from my perspective):
1. Private Equity: Obviously Bain is very strong in PE consulting globally, but this is particularly the case in London which is one of the world's biggest Private Equity markets (and is also particularly hot right now).
2. IT: This is different from digital; most of the work involves helping large companies/government bodies with large-scale IT transformations
3. Retail/Consumer goods: Lots of products in this space, which also tend to be quite analytical
4. Financial Services: It is London, so naturally FS is a big part of the market. Particular strengths are in retail banking and payments.