Really basic maths (and I'll happily be corrected) would tell you that an A330-200 burns about £3,000 of Jet-A1 an hour... So, DOCs might be a distorted argument.
That said, the Head of State and Prime Minister should have a HOS aircraft to represent our country abroad, so if it cost £20,000 an hour it would still be worth the money. We spend money on far more ridiculous things.