Because as he said " it was the right thing to do."
. I have read that article and it all sounds like smoke and mirrors to me. Basically he Co founded Yougov, and would have subscribed to shares in the company at nominal value. His father was entitled also be entitled to shares for helping him set up the company. At some point he disposed of these shares in the last 4 years to this Gibraltar registered company, for a considerable profit which would have triggered a disposal for CGT. But HMRC are quibbling about the exact shares his father was entitled to, which may have been his or his father's. So didn't declare the gain on his shares properly And hence the tax was wrong and underpaid. That's the gist i think.
The Gibraltar company now own the shares, but the ultimate beneficiaries may be his children or grandchildren, not him. Hence why he can say he is not beneficiary of the offshore company. But sure as heck someone on his family is benefitting from the shares.