Liberal Democrat Leader Tim Farron said he will not break bread with "bully" Donald Trump when the US president makes a state visit to Britain later in the year.
Farron also criticised Theresa May for "cosying up" to Trump and pivoting away from European leaders as Britain prepares to trigger Article 50 and begin the formal process of exiting the European Union.
Farron said: "Theresa May might want to cosy up to Donald Trump but I won't. I don't sit down and eat dinner with a bully.
"Her desperate need for a Brexit deal has led her into this mess. She has isolated herself from leaders in Europe and now the irrational new President is all she has.
"I am the one thing Donald Trump hates: liberal, democrat and fighting for a Great Britain that is open, tolerant and united."
The Liberal Democrats have positioned themselves as the UK's anti-Brexit party after Jeremy Corbyn announced he will be imposing a three-line whip on Labour MPs to back the government's Article 50 bill, which is expected to go before both Houses in February.
The Lib Dems are left with only eight MPs after being thoroughly decimated in the 2015 UK general election. They received 7.9% of the national vote, compared with UKIP's 12.7%.
Meanwhile, IBTimes UK has been informed of Jeremy Corbyn's plans to receive Trump if the controversial state visit goes ahead.
A source close to Corbyn said: "Jeremy opposes the State Visit but has said if it goes ahead that he would like to take Donald Trump to Finsbury Park Mosque to show him the contribution Muslims make to the community."