A group of cross-party peers said the government must give “urgent further consideration” to the impact this would have, criticising ministers’ lax approach to the situation.
They wrote: “Our inquiry has demonstrated that any such decision at EU level would have implications for the UK, notwithstanding UK withdrawal from the EU.
“The nature and significance of such implications is not, however, well understood – not least by the government.”
Baroness Donaghy, chair of the committee, said: “So far the government has stuck its head in the sand on the EU Commission’s proposal, hoping that it goes away.
“However, if it doesn’t, we could be caught unaware and unprepared to make a decision, leaving the island of Ireland with two time zones at different times of the year and causing difficulties for people and businesses in Northern Ireland.”
Business minister Kelly Tolhurst, giving evidence to the committee last year, said: “Anything that would create a time border in Northern Ireland we are completely opposed to, and so is the Irish government.”