Of course, the government does not have direct control over the remuneration of private sector firms. They can pay their bosses what they like. And, arguably, it would be too blunt a tool to fix regulations regulating the level of remuneration directors and other senior staff can take home. The Right would also denounce it as a violation of people's economic freedom to operate firms how they like.
However, it does strike me that it is hard to justify anyone getting paid much more than the £200k a year the Prime Minister gets. As such, I would say that much higher income taxes should be introduced on incomes above that figure. If private firms [and remuneration committees in NDPBs and other public sector organisations] want to pay their top people more than that, then they can - but the tax system should tax those earners more, as they are most able to afford it. In addition to the proposed 50% rate, perhaps there should be a 60% or 75% rate on earnings above £250,000.