The Tories have had the best summer ever. First they won a surprise majority. Then their opponents became embroiled in a leadership contest so ludicrous that it preoccupied the media and left them to get on having a proper post-election holiday. When I phoned David Cameron’s MPs for chats during recess, they answered from boats and beaches. Labour MPs answered from the depths of despair.

Now that apparently ludicrous contest has culminated in a backbench rebel becoming Labour leader, the Conservatives must be popping the champagne corks and booking more holidays from which they can relax and read endless headlines about Labour mayhem.

But oddly, the party has seemed rather serious and sad over the weekend, rather than jubilant. Michael Gove was at pains on the Andrew Marr Show to warn about the dangers of Jeremy Corbyn as Prime Minister, rather than chuckling cheerily. Some Corbyn supporters take this, and the official Tory press line that “Jeremy Corbyn is a threat to our national security, our economic security and your family’s security” as a sign that the Tories are rattled by his resounding victory.

Rattled may be too strong a term, but the Conservatives have been giving serious thought about how best to respond to Corbyn’s leadership in a way that strengthens their appeal to voters. Ministers have decided that the best tone to take is “serious and sorrowful”, rather than flippant mockery, hence Gove’s tone. Tory backbenchers were briefed over the weekend to use the word “serious” repeatedly when discussing the new leader of the Opposition.

The Conservatives want to be the first to brand Corbyn’s Labour party, creating an early impression it is difficult for the new leader and his colleagues to shrug off once they’ve organised themselves. They also suspect that Corbyn won’t be the leader for ever, but want to make the most out of his tenure in order to make the Labour brand appear even more toxic to voters than it apparently did during May’s election.

That Corbyn pulled out of his first booked broadcast appearance yesterday gave the Tories an early opportunity to advance this depiction without the new leader being present to rebut it. They can also count on a number of newspapers that were hostile to Labour at the General Election growing yet more hostile now the party has a leader much further to the Left than anything Ed Miliband ever offered.

Indeed, that the newspapers plan to have such a field day with Corbyn means the Conservatives don’t need to resort to much aggressive campaigning themselves. They needn’t use what their general election strategist Lynton Crosby called a “dead cat strategy”, which is to throw something so grotesque and alarming into the public debate that it distracts everyone from anything bad that you’re doing at the time. The press will provide dead cats aplenty, and the Tories should leave them to it.

David Cameron must also be careful not to be too aggressive when responding to Corbyn at Prime Minister’s Questions (when the Labour leader takes this session, that is: he plans to give other colleagues a go at this too). Even if he goes into the Chamber intending to be serious and sorrowful, the Tory leader can, when his blood is up, grow rather jeery and unpleasant. This “Flashman” tendency led to him telling Labour frontbencher Angela Eagle to “calm down, dear”, and calling Ed Miliband a “waste of space” in the last Parliament. He does not want this weakness to help Labourites depict him as a public school bully.

Similarly, the groups of Tory MPs responsible for organising heckling and “supportive” questions in the Commons could border on the unpleasant and aggressive if they’re not carefully controlled. The hurly burly of the Commons means that many MPs behave in ways that surprise even themselves. But overexcited jeers will only help Corbyn paint the Conservatives as the party of dirty old politics.

One Tory minister suggests a clever way of avoiding this, which is to “move on to largely ignoring Corbyn and saying millions of people who voted Labour didn’t vote for his sort of Labour manifesto”. This again means the Conservatives appear seriously concerned about the damage Corbyn could inflict on the country, rather than as though they are bullies trying to hound him out of the Commons.