Since being elected to Westminster in 1997, I have entered the Private Members Bill ballot pretty much every year, so it was a pleasant surprise to be selected for this year's round of bills.

After deliberating over a number of different options, I decided to introduce a Bill to make good on a long-standing Liberal Democrat commitment to enshrine in law the UK Government's spending on aid to developing countries at 0.7% of our Gross National Income (GNI) each year.

I have always been a passionate advocate for international development. As the Liberal Democrats' shadow spokesman for this policy area from 2007 until 2010, I urged the UK Government to fulfil the 0.7% aid target set by the UN. I am proud to have been a member of the first UK government to reach it. Through this Bill, I want to ensure we keep achieving the target and continue to make our contribution to fight hunger, poverty and inequality around the globe.

I won't achieve this important goal on my own, and I don't need to. The LibDems, Labour and the Conservatives each included a commitment to enshrining it in law in their 2010 manifestos and it was also included in the Coalition agreement. The Bill has already gained strong cross-party backing as shown by its list of supporters, including the former Conservative Secretary of State for International Development Andrew Mitchell and Scottish Labour figures such as Anne McGuire and Tom Clarke. I am also pleased that SNP MP Pete Wishart has told me his party will support the Bill as well.

The passage of this Bill will come at a time when UK aid is already making a positive impact on the lives of millions of people across the world. In 2012 and 2013, UK aid gave 19.6 million people access to clean water, 8.7 million people emergency food assistance and helped 5.9 million children - 2.8 million girls - go to primary school.

I could go on but these figures do enough to demonstrate how UK aid helps fulfil the basic needs of millions of people around the globe.Of course, Scotland plays a crucial role in this UK aid effort through the work of the 600 staff at the Department for International Development (DFID) in East Kilbride, as well as a host of charities and other groups that raise funds for and campaign on international development issues.

Some argue that, during challenging economic times, aid should be scaled back and spending should be focused entirely at home. I would disagree. With the refugee catastrophe unfolding in Syria and 1.4 billion people in the world still living in poverty, we have a moral obligation to continue to meet our aid commitments and play our part in providing food, water, shelter and medical help to people in desperate need. This is what UK aid delivers and this Bill would ensure that it continues to do so.

This is not just about the duty of the rich world, but also about its self-interest. In a globalised world problems do not stay local for long. Whether it is financial contagion, environmental degradation, political instability or migration, the problems of the developing world are firmly those of the developed world, too. In this situation, there is no awkward choice between altruism and national interests. The UK benefits when people are lifted out of poverty, economies grow and countries become stable and this is why I believe it is in our own interest to maintain our aid spending at 0.7% of our GNI.

Enshrining this target in law will enable the developing countries we support and the NGOs the Government works with to anticipate the assistance they will receive and plan effectively. There is no doubt that spelling out the UK's aid commitments will also be a powerful tool to leverage outstanding commitments from other donor countries.

I hope the International Development (Official Development Assistance Target) Bill will help us to do just this and ensure that the UK continues to support those around the world who are less fortunate than ourselves.