How about if the UK maintains the Commonwealth of Nations as the basis for an economic common market, instead of drifting towards Europe and the newly established EEC in the 50's (a "Plan H" scenario, as opposed to Eden's "Plan G" to create a European free trade zone while also protecting the favoured status of the Commonwealth, since the British wouldn't have been able to 'have their cake and eat it')? Let's say that the UK gets fed up with repeatedly trying to join the European Economic Community, only to be vetoed over and over again by Charles de Gaulle (persevering for 14 yrs IOTL, before only being admitted after de Gualle's death); giving up on trying to join the EEC in the late 60's, and deciding to push ahead with establishing its own Commonwealth Economic Community instead. Eventually, if this featured freedom of movement, even if it wasn't to the same extent as in the EU IOTL, given the far larger population levels of the Commonwealth relative to the EU and the far greater levels of relative poverty in its most populous states, you'd expect England to be one of their destination of choice (with Australia, Canada & NZ also in the top-tier of Commonwealth migrant destinations under a 'freedom of movement for workers' agreement). And it wouldn't be unrealistic to anticipate 3-4x as many Commonwealth migrants to England as there were EU migrants to England in the same timeframe. And given that there have been roughly 3.5M EU migrants to England, comprising around 6.3% of England's population, in that timespan- with England's population roughly 80% White, excluding these White Europeans (78%, excluding the Scots and Irish)- that'd easily provide enough room to achieve this. Especially if there's significant 'white flight' of White Britons emigrating to other places in the Commonwealth, like Australia, Canada, NZ, Malta, Cyprus, the Caribbean and Polynesia, in addition to all that extra immigration.