British Prime Minister Theresa May's pledge to give parliament a vote on a second referendum if MPs back her withdrawal bill was met with scepticism by pro-EU campaigners outside Westminster on Tuesday.
Two activists, dressed in the EU's distinctive circle of stars, referred to the offer as "hot air" and "fairyland" respectively.
President of Welsh Liberal Democrats William Powell said the likelihood of the prime minister passing her new deal was "unrealistic".
MPs have already rejected the withdrawal agreement negotiated with the EU three times and attempts to find a compromise between the Conservatives and Labour also failed.
May intends to bring her revised plan before Parliament in early June. Apart from a second referendum promise, it also contains guarantees on workers' rights, environmental protections, the Northern Irish border and a customs arrangement.