After months of waiting and the resignation of two defence ministers, the Defence Investment Plan finally appeared last week.

Defence is the first responsibility of any government. In Parliament, it is overwhelmingly a matter that is dealt with on a bipartisan basis, while still requiring scrutiny and challenge.

In East Hampshire, defence is also personal to many. We have strong ties to all of the Services, including through proximity to Portsmouth and RAF Odiham, and until recently the School of Electrical and Mechanical Engineering at Bordon. Many serving personnel, regular and reserve, live here and we have an above-average number of veterans and active cadet groups.

The plans and funding for defence matter very much to the whole country. They have particular significance in our area.

This Defence Investment Plan is an important step and has been hard to reach agreement on within government. But it is only the first, and relatively speaking the most straightforward, step on a journey we must commit to.

Since around 1990, after the Wall came down, not just the UK but many Western nations sought to bank a 'peace dividend' from the end of the Cold War, with money diverted to domestic spending. The September 11 attacks prompted increases again, especially in the US, but by the early 2020s, most Western nations were spending a significantly lower proportion of GDP on defence than they had been in the 1980s.

The world has now become a more dangerous place, with a belligerent Russia, war in Europe and multiple threats and sources of instability around the globe.

The risk register is also more varied. Alongside 'traditional' defence, there is much more to be done against cyber threats, sabotage and other emerging risks. The weaponry, including drones and autonomous systems, is also far more complex and sophisticated.

The truth is that any peace dividend has vanished. We, and our allied nations, need to find significantly more funding to defend ourselves.

The content of the Investment Plan is broad and varied. Ministers have promised an additional £15 billion over the next four years to fund warships, aircraft, nuclear submarines, better protection for undersea infrastructure and significant investment in artificial intelligence and cyber capability.

It is good to see the investment planned for Portsmouth Naval Base, alongside a drone procurement approach informed by lessons from Ukraine.

Some other aspects are disappointing. For many years, we have not done enough to improve the standard of accommodation for service personnel and their families. Although the plan includes a promise of much-needed work to military housing, it appears the timetable has been pushed back further.

To make the numbers work, there are some heroic assumptions about the 'efficiencies' that can be found elsewhere in the budget, and about reducing fraud and error in procurement, which is always important to pursue but harder to bank. Moreover, almost £5 billion is still to be found during the tenure of the next Prime Minister. Even the funding that has been confirmed relies on capital cuts being made elsewhere, some of which may prove difficult to achieve part-way through programmes.

Yet these challenges will soon look small compared with what is to come. Reaching defence spending of 3.5 percent of GDP by 2035 will require many times the additional investment that has just been announced.

This sort of increase will certainly not be found through efficiencies or by trimming road improvement budgets. With tax already at a historic high, there will have to be a difficult debate about how we prioritise public spending as a country.