Oliver Dowden claimed Mr Sunak was simply using “robust language” when he suggested Keir Starmer was a terrorist sympathiser earlier this week.
Mr Dowden said Mr Sunak was highlighting the fact that when he was a lawyer Sir Keir had represented the group Hizb ut-Tahrir, which the government has proscribed.
“I would say that is the use of robust language. I wouldn't say that was the prime minister misleading," he said, as he also denied the government lied.
His claims come just weeks after Rishi Sunak was rapped by the official statistics watchdog for repeatedly claiming to have “cleared” the asylum backlog.
The UK Statistics Authority told the prime minister his assertion risked eroding trust in the government.
Meanwhile, Lord Rose, the boss of the retail giant, attacked what the British people were told about leaving the European Union.
Following reports Brexit has cost the UK economy £140billion so far, Lord he told LBC: “The short answer is, we were lied to, we were gullible. We voted for it. And we now have to pay the consequence.”
He added: “I don't want to say I told you so, I was a very minor voice in a very difficult campaign when frankly, we were lied to. Where is the £300 million for the National Health Service? Where is the membership of Turkey to the EU, which was going to flood the EU with immigrants? Now we've got an immigration problem, which was caused by different things.”
The prime minister said the "the facts speak for themselves" when asked if Sir Keir Starmer is a terrorist sympathiser.
Mr Dowden said he believed in “robust political discourse” but added “what I don't believe in and have never believed in is lying or misleading people. Because in the end, I think you damage yourself and you do damage politics at large."
Asked "so you don't think at the moment your party is doing that?", the deputy PM replied: "No, I don't, no."