The UK needs to look at Brexit with "cold-eye" realism, EU commissioner Phil Hogan has warned.
In a hard-hitting speech to the Seanad, Mr Hogan criticised the UK for being delusional about its split from the EU.
He also claimed Theresa May's government was trying to "invent" an unworkable solution for the border.
Mr Hogan said: "We are still stuck fast in the UK's self-imposed contradiction between its reassurance of a soft border and its hardline demands, its red lines, which have led the EU to offer a free-trade agreement.
"The UK wants to keep its red lines, understands that a free-trade agreement means a hard border, and is trying to escape by 'inventing' a new type of border."
Mr Hogan, Commissioner for Agriculture and Rural Development, claimed the UK had to face up to the fact that the Brexit deadline was looming.
He added: "The European Union has looked at the UK and their ideas, it is not convinced that they can give us the border security we need within the Brexit timescale and has sent the UK back to the drawing board, meanwhile it insists on the backstop of a customs union for the whole of island of Ireland.
"An Taoiseach and the Government, supported by all parties in this House, supported by the European Union, have made it clear that they are not fudgers.
"The UK has to face up to the fact that decision time is here.
"The European Union must be satisfied that the UK's invention will work or it is the backstop that will be implemented.
Meanwhile, there were also harsh words for hardline Brexiteers.
He added: "The recent statement by Jacob Rees-Mogg in relation to Irish beef is a good example of a comment that is both unhelpful and irresponsible.
"But of course this is his stock-in-trade."