Biden’s capital gains tax reforms could boost HMRC revenues Biden’s capital gains tax reforms could boost HMRC revenues US President Joe Biden’s tax plans could incentivise US citizens based in the UK to disclose assets Author Categories US President Joe Biden’s plans to increase capital gains tax in the US might see an increase in UK tax revenue as American citizens may declare income in the UK for tax credits, according to Adam Bonnell, tax partner at HW Fisher. Biden presented his American Family Plan on Wednesday, proposing an increase in capital gains tax to 39.6 percent for households earnings more than $1m per year, up from 20 percent.