I'm pretty sure that UK will act unilaterally about this pretty soon. Once they're out of the EU, there's no reason for them not to tax the UK profits of EU companies, is there?
Assuming we ever actually get "out of the EU", then the rEU become our competition for tax revenues. There's nothing to stop us attracting their companies here by ensuring our rate of Corporation Tax is lower than theirs, thus getting a slightly smaller slice of a much larger pie. In essence, lowering the rate in order to increase the revenue extracted.