The number of EU and EEA citizens that interact with HMRC through payment of Income Tax or National Insurance Contributions, or receipt of tax credits or Child Benefit, is available in the publication “Income Tax, NICs, Tax Credits and Child Benefit Statistics for EEA Nationals, 2014 to 2015”. The statistics are available on gov.uk at the following location:
Table B1 (page 10) provides information on Income Tax, National Insurance Contributions, tax credits and Child Benefit with a breakdown by EU country, and aggregates for EEA and EU. Table D1 (page 14) shows the total number of non-UK EEA nationals with a tax record.
These tables show that in 2014-15, 580,000 EEA nationals were claiming tax credits and there were 2,870,000 EEA nationals with an Income Tax record.