I have no idea what percentage of EU migrants are lower earners but suspect it is most of those in the agricultural sector, catering and retail. To pretend that some bloke on minimum wages or more likely zero hours contract is paying down the national debt is ludicrous. They'll be paying little or no tax and NI.
EU immigrants are more educated, younger, more likely to be in work and less likely to
claim benefits than the UK-born. About 44% have some form of higher education
compared with only 23% of the UK-born. About a third of EU immigrants live in London,
compared with only 11% of the UK-born.
Many people are concerned that immigration reduces the pay and job chances of the UKborn
due to more competition for jobs. But immigrants consume goods and services and
this increased demand helps to create more employment opportunities. Immigrants also
might have skills that complement UK-born workers. So we need empirical evidence to
settle the issue of whether the economic impact of immigration is negative or positive for
the UK-born.
EU immigrants pay more in taxes than they take out in welfare and the use of public
services. They therefore help reduce the budget deficit. Immigrants do not have a negative
effect on local services such as crime, education, health, or social housing
AND
Long-term fiscal impacts of immigration
In 2013 the Office for Budget Responsibility (OBR) examined how the long-term fiscal sustainability of the UK might change over a 50-year period, depending on the level of migration to the country and expecting the same fertility rate for migrants and the UK born population.
Unlike the studies discussed above, the long-term estimates look at the fiscal impacts of at anticipated future migration flows, rather than migrants who are already in the country; they also implicitly account for the impacts of migrants' children once they enter the workforce. The OBR found that:
Higher net migration would reduce pressure on government debt over a 50-year period. Based on OBR projections, the high net-migration variant.
This result was driven by the fact that incoming migrants are more likely to be of working age than the population in general. The OBR noted that over an even longer time horizon than 50 years, these migrants would also retire and add to age-related spending pressures.
It concluded that "higher migration could be seen as delaying some of the fiscal challenges of an ageing population rather than a way of resolving them permanently".
http://cep.lse.ac.uk/pubs/download/brexit05.pdf
https://fullfact.org/immigration/how-immigrants-affect-public-finances/
Osborne's whole strategy revolves around a growing economy to pay down the deficit. His positive economic forecasts for 2030 inside the EU depend on the number of EU migrants actually growing not shrinking.