Gulp. It's the Home Office

"Gulp". That was the reaction from one of Shabana Mahmood's team when news broke that she was heading to the Home Office. Gulp indeed. Mahmood has done well at the Ministry

of Justice (MoJ), but the challenges at the department down the road are of a different order.

Yvette Cooper, my boss when I worked in Labour's home affairs team in Opposition, laid solid foundations during her 14 months as Home Secretary. Moves to strengthen and fund neighbourhood policing; the impressive immigration White Paper, which charted a clear path to reduce the UK's reliance on overseas labour; and the establishment of the Border Security Command, with greater international co-operation on smuggling gangs, are the key changes Cooper put in place. But they weren't enough.

Politics, these days more than ever, is a 'results now' business. And the results simply weren't visible - with more than 50,000 migrants crossing the Channel in small boats since Labour came to office and 32,000 asylum seekers still living in hotels. Over time, it's possible, that the crossings might come down - if the one-in, one-out deal with the French government that Cooper successfully negotiated proves to be a deterrent. But time wasn't on her side.

For Number Ten, the row over the Bell Hotel at Epping was doubtless the final straw. The Home Office was slow to respond to the legal attempt to close the Essex hotel, which houses 138 asylum seekers, and in the final weeks of August it appeared that ministers had lost their grip on the situation, vanishing from the airwaves and allowing the vacuum to be filled by Reform UK and Nigel Farage. The Prime Minister will be hoping that Mahmood's punchy style of communications will help get the Government's message across more effectively, while her approach to policy-making, which relies as much on instinct as it does on evidence, will sharpen their response to the problem of boats and hotels.

At the MoJ, the 44-year-old Birmingham MP skilfully avoided a backlash over her decision to free offenders from prison early. She had set out the case convincingly, citing the Conservatives' abject failure to match prison cell capacity to tougher jail terms, and commissioned three independent reviews to provide the political and legal 'cover' for radical reforms to sentencing, prisons and the courts. Appointing the respected former Tory Justice Secretary, David Gauke, to conduct the most politically tricky review, into sentencing, was a clever move, as was the briefing around the findings which included a tabloid splash about chemical castration for sex offenders.

The dispute over guidelines on pre-sentence reports issued by the Sentencing Council was a further example of Mahmood's political nous. Although I think she over-reacted - and lost some respect in the judiciary as a result - when she moved swiftly to legislate to ensure the guidelines didn't take effect, her actions outflanked Robert Jenrick, the Tories' Shadow Justice Secretary. (It will now be up to the former Foreign Secretary David Lammy to take the fight to Jenrick and the 'two-tier' justice campaigners. Lammy, a barrister who briefly shadowed the MoJ in Opposition and wrote a landmark report about the treatment of ethnic minorities in the justice system, is ideal for the job - a compelling public speaker and charismatic communicator, his oratorical talents are more suited to domestic policy than to foreign affairs).

Prisons dominated Mahmood's period at the MoJ, but at the Home Office there are banana skins in every corridor. From the fallout from her predecessor's decision to proscribe Palestine Action as a terrorist group, to the epidemic of shop theft; from concerns about police funding, to the forthcoming inquiry into 'grooming' gangs - these are all her responsibilities now, along with national security which will consume much of her time. There is also unfinished business from Cooper's tenure.

A strategy on violence against women and girls, setting out how the government aims to achieve its target of halving offences in ten years, should have been issued in July but is still awaited. Suggestions that Mahmood was less than impressed with draft versions circulated earlier this year could delay it further. There is yet to be a comprehensive plan on halving knife crime, the Government's other main law and order target, while policing leaders are impatient for the promised White Paper on police reform. I understand the document has been largely written, with publication scheduled for November, but the arrival of a new Home Secretary might prompt chiefs to push her to be bolder about altering the structure of the service and the 43-force model.

Then there are boats and hotels. Mahmood will know that success as Home Secretary - and for her Government - depends on making tangible progress on both. Until now, Ministers have talked a lot about ending the use of asylum hotels, offering vague promises and snippets of ideas, but they haven't set out any concrete measures to show how they will do it. No detailed timetable, no figures, no plans. That has to change.

The establishment of a new Home Office Asylum Task Force, with input from Downing Street and the Ministry of Defence, is a sign that the Government has belatedly realised that it needs significantly more firepower in this area. That decision was announced shortly before the appointments of Mahmood and two young, energetic ministers, Alex Norris, who will oversee borders, and Mike Tapp, a former soldier and National Crime Agency officer, but it is long overdue, and should help re-set the department so that ending hotel use is an objective in itself, rather than a by-product of wider changes to the asylum system.

If, for example, the Government were to close five asylum hotels every month over the next two years they would be well on the way to ending their use altogether, demonstrating to the public that they can achieve results. That's what Mahmood will primarily be judged on. Gulp.