Figures published today show the Conservatives have delivered on their 2019 manifesto pledge to recruit 20,000 police officers, which Rishi Sunak and Suella Braverman are trumpeting as the two main parties continue their war of words on crime. There’s only one problem: today’s numbers merely reverse previous cuts by the Tories after they took power in 2010.

Unusually, both the Conservatives and Labour are currently happy to campaign on crime – traditionally, strong ground for the Tories. Keir Starmer’s aides are convinced his record as director of public prosecutions (DPP) between 2008 and 2013 means Labour can win on the issue and exploit the Tories’ patchy performance in the last 13 years. This includes a worryingly low number of reported crimes, including rape, resulting in a charge or summons and a huge backlog in the courts, including for sexual assault cases.

But some Labour MPs privately fear the party’s attack has boomeranged because of its controversial ad claiming Sunak does not think paedophiles should go to prison. Labour politicians don’t really believe that, and give the game away in media interviews: when asked whether they think the statement is true, they avoid the question. “It’s legitimate to go in hard but we can’t tell lies,” one Labour MP told me. “The hard stuff works only if you tell the truth”. True. Defenders of Labour’s ad insist it disrupted the government’s narrative that Sunak is fixing the problems he inherited, and forced the Tories onto the defensive on crime; they argue that Labour needs to ensure Sunak “owns” the Tories’ record, so voters do not see him as a “fresh start”. This reflects jitters behind the scenes in Labour land because Sunak’s ratings are higher than his party’s, and because he has slightly eroded Labour’s opinion poll lead.

However, there is also concern inside Labour that Starmer has locked the party into a bidding war with the Tories on ever-tougher sentencing. That’s not even what the “lefty lawyer” depicted by the Tories believed in his former life, according to some of Starmer’s former colleagues at the time. They recall he recognised the need for courts to have the option of non-custodial sentences and for judges not to have their hands tied by parliament.

Team Starmer confidently trumpets his record prosecuting terrorists, grooming gangs, sex offenders, people smugglers and other criminals, but it has invited close scrutiny of his time as DPP. I think this might not be the one-way street they imagine. If Starmer is going to claim credit for his undoubted successes as DPP, he is bound to be challenged about the failures under his leadership (even if he was not directly responsible); he can’t really have it both ways.

Although the Tories were always going to play the man rather than the ball come the general election, Labour’s personal attack on Sunak has given them licence to hit back now.

Even if the Tories don’t say it, we can expect their newspaper cheerleaders to raise the failure to prosecute the child abuser Jimmy Savile (Starmer was not the reviewing lawyer, but did apologise on behalf of the Crown Prosecution Service) and claims he overcompensated for that by bringing in a culture in which alleged abusers were guilty until proved innocent (Starmer allies blame this on the police). The Tory-supporting papers may also press Starmer over whether he ever took drugs. It has already begun, and things can only get nastier. Some senior Labour figures would prefer a clean fight on policy rather than see their party descend into the gutter with the Tories. “The danger is that voters think we are all the same,” one told me. Despite Starmer’s genuinely impressive backstory, such critics doubt whether Labour can really win on crime. If Labour is going to go in hard, they would prefer attack ads about the NHS, recalling the “War of Jennifer’s Ear” at the 1992 election.