According to Boris Johnson, the backstop is unacceptable, since it is "anti-democratic and inconsistent with the sovereignty of the UK as a state."
"The UK and the EU have already agreed that 'alternative arrangements' can be part of the solution. ... I propose that the backstop should be replaced with a commitment to put in place such arrangements as far as possible before the end of the transition period, as part of the future relationship," the prime minister said in a letter published on the UK government's website.
The Irish border issue has been a stumbling block in the EU-UK Brexit talks. In November, Brussels and London agreed on the Brexit deal, including the so-called backstop that would be put into practice if the sides failed to agree on all the terms of their relationship by the end of the Brexit transition period.
Johnson made it clear that he wanted the United Kingdom to leave the European Union on October 31 "come what may," although he said he preferred an orderly exit. He has been calling on the European Commission to drop a clause that seeks to avoid a hard Irish border by tying the country to the EU customs union, despite Brussels saying it will not reopen the talks on the Brexit deal.