Last night saw Conservative election tactics reach a depressing new low. The optimism of Tuesday's manifesto launch was gone - replaced by lies, spin and an attack on good manners. As the BBC debate was broadcast, the party reached a nadir.

Failure to attend

It all began, of course, with David Cameron's failure to attend the debate. Downing Street used every weapon in its arsenal to avoid the TV debates, engaging in a drawn-out and bitter war of words with broadcasters.

Cameron's refusal to participate was ultimately an act of disrespect to the public. After all, the public want the debates – that much is clear from the impressive viewing figures they attract. And, importantly, they do not seem to just attract the usual political obsessives either. The second most-searched for term last night was: "Why is David Cameron not at the debate?" Clearly, this is an audience which did not follow the tedious ins-and-outs of the debate over the debates. But they wanted to know why they couldn’t hear from the prime minister as he ran for re-election.

The most searched for term - "what is austerity?" - was also instructive. It demonstrates how TV debates attract voters who are not usually tuned into politics. During an age of mass disenchantment with Westminster, it is criminal for a politician running for elected office to refuse to participate in a format which shows such strong levels of public interest.

Lying

Having decided their candidate would not attend, the Conservative party then start lying. Cameron claimed – laughably – that he had not been invited. Before the debate he said:

"I'm a polite individual and if I'm not invited, I'm not going to try and gatecrash it."

It's a lie. There's no other word for it. The broadcasters wanted Cameron in three TV debates. He refused to do more than one, and then only with seven party leaders on stage.

William Hague was sent out to repeat the lie in the spin room. Together with being forced to launch an underhand, last-minute attack on John Bercow, the former foreign secretary has ended his political career in the most unsatisfactory manner. He has good reason to feel aggrieved by the positions he's been pushed into as he looks forward to his retirement. If he's lucky, biographers will skip over these two inglorious episodes.

On Question Time later, Grant Shapps/Michael Green was at it again. The lie about Cameron's attendance wasn't just the product of the prime minister. It was formulated and issued straight from Tory HQ.

The spin operation

Cameron must have been the only senior Tory figure not attending the debate. The spin room was rammed with them. Three Tory ministers were there – Hague, Jeremy Hunt and Liz Truss – along with the rarely-seen Craig Oliver, head of communications.

Tory MP Liz Truss having to defend Cameron's non-show from journalists pic.twitter.com/HpTfrzC5TL — Sunny Hundal (@sunny_hundal) April 16, 2015

The broadcasters should not have let them in. They weren't part of the debate. Under what basis were they entitled to propagandise about it on-site? If the broadcasters were going to start allowing people who had nothing to do with the debate on, why stop there? Why not invite the local vet and some baristas?

My inbox was rammed by emails from the Tory press office – far more than I received from any of the parties in attendance. It was an absurd sight to see a party exclude itself from a debate and then furiously try to participate once it started.

Most emails – and the majority of the spin operation – were dedicated to emphasising the struggle between Labour and the SNP. The Tories hyped the performance of Nicola Sturgeon in a bid to suggest she would out-manoeuvre Miliband in a coalition or confidence-and-supply arrangement. They pointed to the debate as evidence of what left-wing coalition negotiations would look like. They were trying to weaponise their absence.

The sad thing is many journalists let them. Instead of treating their absence as the story – or at least ignoring their contributions on the basis of it – most papers led with the Miliband-Sturgeon angle. But there was no new development last night. Going into the debate, Labour and the SNP both said they would not do a coalition, but would not rule out a less formal arrangement. Going out of the debate, that remained the case. Nothing changed. There was no news. But Tories pointed at it and journalists dutifully reported it.

Attacking handshakes

But the most dishonourable part of the Conservative response to yesterday evening came at the end, when the party took a screen grab of Miliband shaking the SNP leader's hand and tweeted it out as if it were a warning of things to come.

Already shaking hands on the deal. Don't let it happen #BBCDebate #VoteConservative pic.twitter.com/JjJzINgizU — CCHQ Press Office (@CCHQPress) April 17, 2015

This is what the Conservative party has come to: attacking common courtesy. Perhaps they would have preferred it if Miliband spat on her and pulled her hair.

Politics is always full of cheap tricks. That is part of its currency. But the tweet spoke to something much deeper in the Conservative campaign, a lack of honour or basic decency in the way it is conducted.

This is a process which Cameron is partly responsible for. He made the attacks on Miliband personal throughout the last parliament, constantly berating him for his supposed weakness, mocking him for making Ed Balls cups of coffee, or highlighting how weird he is. The tactic has been ingested and repeated by the party, from the ministerial level to the ground troops. It resulted in Michael Fallon's inane attack on Miliband having stabbed his brother in the back and preparing to do the same to his country – an attack which was not just personal but also questioned the Labour leader's patriotism, an area which should always be out-of-bounds in civilised political discussion.

They may have tried to go positive earlier this week, but yesterday's behaviour suggests the Tory party remains stuck in the gutter in this election. If it's criticising people for shaking hands after a debate, it needs to take a long, hard look at itself and remember a motto which many of its MPs would have seen in school: Manners Maketh Man. There's still time to raise the standard of debate in the next three weeks. For all our sakes, the Conservatives should resolve to do that.