Former Irish prime minister Bertie Ahern has criticised Theresa May's decision to trigger Article 50, saying the move was "absolutely senseless".
The prime minister had made a number of "tactical errors" over Brexit, he told BBC Radio Ulster's Inside Politics programme.
Her "biggest mistake" was triggering Article 50 "before [she] had worked out the strategy", he added.
"It wasn't necessary and it has by and large led to where we are today."
Mr Ahern, who was taoiseach from 1997 until 2008, said Mrs May's mistakes included calling a general election in 2017, when the Conservatives lost their parliamentary majority and leading to their reliance on the support of the Democratic Unionist Party (DUP).
"There was absolutely no need to call an election," he said.
He also criticised Mrs May's failure to engage earlier with party leaders over Brexit, adding that he could not understand why she "waited to the 11th hour" before talking to them.
He said: "Normally in negotiations, you would be trying to get parliamentary support, either by leaders directly or by the whips."
He also suggested that since Christmas Mrs May had allowed Westminster opposition to her Brexit deal to grow.
'Narrow down ideas'
On what Mrs May needs to do next, he aid a series of options should be presented to MPs in the House of Commons.
He said the best way to find a way forward on Brexit was to "narrow down the ideas" in a series of parliamentary votes.
He suggested that a number of Commons votes on options could be done quickly.
"My suggestion could be done in about four hours," he said.
But former Northern Ireland Secretary Theresa Villiers told Inside Politics that a series of votes on different Brexit options would not work.
"We don't need a list... I don't think a list of options would take us further," she said.
On the issue of a 'sunset clause' to the Irish border backstop plan, Ms Villiers, who campaigned to leave the EU, said she was "prepared to look at compromise".
She said that if the backstop was time-limited she would "look at it seriously".
The prime minister has been meeting cabinet members to discuss the next steps after her Brexit plan was overwhelmingly defeated this week.
She held talks with some party leaders about a way forward after she won the confidence of the House of Commons in a vote on Wednesday.
The Labour Party leadership has ruled out meeting the government for Brexit talks until the prospect of a no-deal withdrawal is taken off the table.
However, Mr Ahern has criticised that position, saying that Labour leader Jeremy Corbyn should meet Mrs May.
He said that "making preconditions in negotiations is never a good idea" and claimed that doing so "usually works against you in the end".
Inside Politics airs on BBC Radio Ulster at 18:05 GMT on Friday 18 January and is repeated at 13:30 GMT on Saturday 19 January.