The relentless rise of cable was anyway eroding that (three out of four new Sky subscriptions now come from cable).

ECONOMIST: Digital television

Although he warned that Labour was "probably playing political games" by backing a mansion tax, the policy was "an idea whose time has come", Mr Cable told Sky News.

BBC: Lib Dems look at extending mansion tax

Broadcasters and cable TV providers including Sky, Virgin and BT are also increasingly offering on-demand services.

BBC: Netflix to launch film streaming service in UK