The 10.45% stake he had when NTL and Telewest merged and under the Virgin Media moniker in 2006 was reduced to around 6.5% in May 2009 according to this
article.
Wikipedia says:
I
n July 2007, Virgin Group hedged 37% of its stake in Virgin Media for $224m through a collared loan agreement with Credit Suisse, a transaction which enabled it to retain the voting and dividend rights. Virgin Group had the option of buying back the 12.8m Virgin Media shares it had mortgaged after two years, but in May 2009 decided against this. The funds were used at the time by Virgin Group to invest in other areas of its business, such as Virgin Green Fund, which was launched in September 2007, Virgin America and Virgin Mobile India. By December 2009, Sir Richard Branson's Virgin Entertainment Investment Holdings Limited held a minority holding of 21,413,099 Virgin Media common stock, making him the third largest shareholder.
When Liberty swooped in 2013 to buy VM he held 6.6m shares according to this
article - worth £202m and paid as £67m in cash in £135m in Liberty shares.
Plus of course the £10m or so he makes per year from the branding.