A bitter political wrangle between Swiss and EU authorities, which could force stock exchanges to halt trading in Swiss stocks within days, is a step back in time to before EU rules spurred competition – and cheaper trades for investors – across the continent, market watchers say.

Tit-for-tat moves by regulators, with a June 30 deadline looming, mean investors across Europe might find they are unable to trade Swiss shares — including blue-chip multinationals like Nestle and Novartis — on EU markets. Around 30% of Swiss shares are traded outside the country at present; mostly in London.