The term 'castling' is a chess move intended to protect the king from attack. Castling is something that politicians are constantly practising. Take G4S for example.
G4S is a security company that was an amalgamation of a couple of companies and has a number of politicians with vested interests, not least the prime minister Theresa May who has shares in Prudential which is a major shareholder in G4S. The passage below is from a Channel 4 news programme and sums up the massive vested interests of the government with certain private companies.