Ed Miliband has accused David Cameron of becoming so distracted by the need to control dissent within his divided and "backward-looking" party that he is unable to govern effectively.
Writing exclusively for The Huffington Post UK on Tuesday, the Labour leader said: "Last week we watched his government being pushed around by Conservative backbenchers so that on the crucial issue of Europe policy now appears driven by the short term political interests of internal party management rather than the long term interests of British businesses and British workers.
"This week we have watched the prime minister looking desperately over his shoulder at the MPs behind him over the issue of same-sex marriage
"Being backward-looking and inward-looking will not work if we are to succeed as a country and meet the new challenges presented by the digital age."
Miliband added: "The events of the past three weeks have only served to underline how distant and distracted David Cameron, not to mention his divided party, has become from addressing these issues."
The prime minister has come under intense pressure from within his own party in recent days, from both the activist base and backbench MPs unhappy with his style of leadership and determination to enact gay marriage.
Cameron took the unusual step of writing to all party members last night to strongly deny one of his close aides had referred to the grassroots of the party as "swivel-eyed loons".
The prime minister was also forced to turn to Miliband to rescue the same-sex marriage bill from a backbench Tory "wrecking" amendment last night which he feared could have killed off the legislation.
The Commons is in recess again from tomorrow, meaning Cameron will once again not have to take on Miliband at prime minister's questions. The Labour Party has accused him of "running scared" from a rebellious parliament and tough questioning from the Opposition.
In his article for HuffPost UK, the Labour leader also expressed "surprise" that the prime minister had failed to raise the issue of tax avoidance with Google chairman Eric Schmidt during a meeting in Downing Street on Monday. Miliband said: "Google shouldn’t be going to extraordinary lengths to avoid paying its taxes."
Schmidt is likely to be in for a rough ride when he appears alongside Miliband at a Google 'Big Tent event' on Wednesday.
In a taste of what Miliband is likely to tell the Google chairman, he said the firm had "to do more than simply comply with the letter of the law" and had "an obligation to wider society and to live up to its own founding principles" of 'don't be evil'.
He added: "Think about someone on benefits, who could work, but isn’t doing so. If they were meeting their requirements to report to the job centre, but were only making the barest effort to look for work, we would condemn their behaviour. Well, similarly, companies have obligations that go beyond the law."
The internet giant was on the receiving end of a withering attack by Labour MP Margaret Hodge, the chair of the Commons public accounts committee, who told a senior Google executive: "I think that you do do evil."