Asos co-founder Quentin Griffiths is suing accountancy firm BDO, claiming it give him incorrect tax advice.
Griffiths said BDO was “negligent” and made a “basic and fundamental error” that cost him more than £4m, the Times reports.
In 2013, Griffiths was seeking to sell Asos shares and wanted to avoid capital gains tax. He argues he was advised he could spend 90 days a year in Britain without being liable for tax, when the correct figure was 45 days.
Griffiths launched Asos, then known As Seen On Screen, in 2000 with co-founder Nick Robertson.