However he was almost upstaged by his own cat – who made her own fashion statement in the embassy windows wearing a collar and striped tie, while her owner faced his questioners.

Assange complained that his Swedish counsel Per Samuelson had not been invited to attend the interview – though he did have an Ecuadorian counsel.

"This clear breach of process did not stop Assange cooperating fully… (he) felt compelled to participate," his lawyers said in a statement – but added "these irregularities will be raised in a formal setting in the near future".

This suggests his legal team could challenge the admissibility of the interview as evidence in any future legal action.

Assange's team said he agreed to the interview "in part to ensure the Swedish authorities have no further excuse not to discontinue their investigation".

Swedish assistant prosecutor Ingrid Isgren was present at the interview, which was conducted by an Ecuadorian prosecutor.

She arrived at the embassy at 9.30am, took an hour's lunch break then left just before 6pm.

Assange's legal advisor Jennifer Robinson, an Australian human rights lawyer, said afterwards her client had taken the whole day to give a statement to the Swedish authorities – "but unfortunately there have been a lot of irregularities in the process to date".

The fact that Swedish prosecutors were present but not the Swedish defence counsel was "incredibly problematic", she said – but they had decided to proceed anyway.

"We have been offering his testimony since 2010 and the Swedish prosecutor has refused to hear his side of the story until now."

"We want this process to be over… he has fully cooperated with the process so far.

"He's obviously very pleased that he is finally able to give this statement... the Swedish prosecutor could have had this testimony six years ago and instead she has dragged her feet, refused to take it and left him in circumstances which the UN has found to be… arbitrary detention."

She said she hoped the process would finish on Tuesday – however there is provision for it to continue another day.

And she hoped the prosecutors would then decide to close the investigation.

Those present during the day's statement included Assange's Ecuadorian defence counsel, and the Ecuadorian and Swedish authorities.

"His health has deteriorated seriously in the four and a half years he has been stuck inside the embassy," she said. "Experts have said he is not capable of giving testimony."

Sweden's prosecutors said they would request a DNA sample from Assange.

Asked if he had given the sample, Ms Robinson said "we will be giving more information tomorrow, today he has given his statement".

The Swedish Prosecution Authority issued a statement on Monday evening saying the interview will continue on Tuesday, and that it was "subject to confidentiality".

The results of the interview will later be reported from Ecuador to the Swedish prosecutors in a written statement.

After this report, the Swedish prosecutors will decide whether to continue their investigation or terminate it.

However even if Sweden drops the case it is unlikely Assange would immediately leave the embassy, as he also faces arrest in the UK for breaching his bail conditions.

Ms Robinson said he had a legal right to pursue asylum while on bail and "we will deal with that when we get to it."

It is more than six years since a Swedish prosecutor first ordered the arrest of Assange on suspicion of rape and molestation.

He sought asylum at the embassy in June 2012, after British courts ordered his extradition to Sweden.

Since then Assange and the Swedish authorities have argued over whether, when and how he could be questioned, with the Swedes arguing an interview at the embassy would "lower the quality of the interview", and Assange demanding assurances that Sweden would not extradite him to the United States.

Last year Sweden dropped several lines of the investigation into claims of sexual assault, due to the statute of limitations.