Britain's foreign secretary, William Hague, labelled President Bashar al-Assad "delusional" on Sunday after the Syrian leader attacked the British government for its "shallow and immature rhetoric", which he said highlighted a "tradition of bullying and hegemony".

In an interview with the Sunday Times, many of Assad's remarks were aimed at the British government, which has taken the lead in Europe in pushing for the easing of the ban on arming the rebels. Assad accused the UK of resuming a "bullying" colonial role.

Hague responded by telling the BBC's Andrew Marr Show: "This will go down as one of the most delusional interviews that any national leader has given in modern times."

In the interview, Assad qualified the offer of peace talks made last week in Moscow by his foreign minister, Walid Muallem, saying it was restricted to those opponents who laid down their weapons. He described all rebel forces in Syria as al-Qaida terrorists.

"We are ready to negotiate with anyone, including militants who surrender their arms. We are not going to deal with terrorists who are determined to carry weapons, to terrorise people, to kill civilians, to attack public places or private enterprise and to destroy the country," Assad said. "Opposition groups should be loyal and patriotic to Syria.

"The British government wants to send military aid to moderate groups in Syria, knowing all too well that such moderate groups do not exist in Syria; we all know that we are now fighting al-Qaida or Jabhat al-Nusra, which is an offshoot of al-Qaida, and other groups of people indoctrinated with extreme ideologies. This is beyond hypocritical," Assad said.

Following warnings from Hague last week that he would not rule out supplying arms to the opposition, Assad attacked the British government for its "shallow and immature rhetoric", which he said highlighted a "tradition of bullying and hegemony".

The idea of the UK helping broker a peace deal was like expecting "an arsonist to be a firefighter".

"I am being frank," the president said. "How can we expect to ask Britain to play a role while it is determined to militarise the problem? How can you ask them to play a role in making the situation better and more stable, how can we expect them to make the violence less while they want to send military supplies to the terrorists and don't try to ease the dialogue between the Syrians."

The interview followed a few weeks during which hopes rose that peace negotiations might be possible. The National Coalition leader, Moaz al-Khatib, said the rebels would be ready to enter talks without their earlier insistence that Assad step down first. But he said that more than 160,000 political prisoners should be released as a precondition.

Opposition leaders have since become more confident that the western embargo on arms deliveries to their forces is about to collapse, pushing the balance in a deadlocked conflict in their favour. In his remarks on Sunday, Hague repeated his belief the weapons ban was not sustainable if the bloodshed continued.

"I don't rule out anything for the future. If this is going to go on for months, or years, and more tens of thousands of people are going to die, and countries like Iraq and Lebanon and Jordan are going to be destabilised, it is not something we can ignore," the foreign secretary said.

"If ever we get into that situation [of supplying weapons to the opposition] the risks of arms falling into the wrong hands is one of the great constraints. And it is one of the reasons we don't do it now. But these things are a balance of risk. You can reach consensus eventually when humanitarian need is so great and the loss of life is so great that you have to do something new to save lives. That's why I don't rule it out in the future.