Major General Jonathan Shaw, the former chief of cyber security at the Ministry of Defence (MoD), said on Monday that giving intelligence agencies the ability to spy on messages sent over services like WhatsApp would simply lead to the problem to "mutate and move on".
Rudd said yesterday she supported end-to-end encryption but said security services must be able to eavesdrop when they have a warrant.
The home secretary told the BBC's Andrew Marr programme it was "completely unacceptable" that messaging services provided "a secret place for terrorists to communicate with each other".
General Shaw told BBC Radio 4's Today programme this morning he suspected there was "politics at play" in Rudd's comments, given ministers were currently attempting to justify its Snooper's Charter which gave the government new surveillance powers.
"I think what they are trying to do is use this moment to nudge the debate more in their line," he said. "We are in real trouble if we apply blunt weapons to this, absolutist solutions.
"There's a debate in Parliament about the whole Snooper's Charter and the rights of the state and I think what they are trying to do is use this moment to nudge the debate more in their line."
Khalid Masood, who carried out the attack on Westminster, is reported to have used the app seconds before mowing down pedestrians at speed and storming the parliamentary estate armed with two knives last week.
WhatsApp said in response that it had been assisting the police investigation. A spokeswoman said: "We are horrified at the attack carried out in London earlier this week and are co-operating with law enforcement as they continue their investigations."
Rudd told Marr: "We need to make sure that organisations like WhatsApp, and there are plenty of others like that, don't provide a secret place for terrorists to communicate with each other.
"It used to be that people would steam-open envelopes or just listen in on phones when they wanted to find out what people were doing, legally, through warrantry.
"But on this situation we need to make sure that our intelligence services have the ability to get into situations like encrypted WhatsApp."
Her call for access was branded "draconian" by one former Metropolitan Police deputy assistant commissioner.
Lib Dem Lord Paddick said: "The real question is, could lives have been saved in London last week if end-to-end encryption had been banned? All the evidence suggests that the answer is no."