Let me dismiss out of hand some of the implausible explanations generated by the Conservative Central Office propaganda machine in the past 48 hours. I can assure readers of the Independent that it has not been out of "ambitious careerism" or "personal pique".
These attempts at trivialisation of what has been an agonisingly difficult personal decision are unworthy, although perhaps not surprising. But they also underestimate the nature of the crisis that besets the Government of this country and our whole political system, which have led me to this decision.
The Conservative government led by John Major seems paralysed by indecision, waiting for an election which cannot long be delayed and relying increasingly on the worst, hard-faced, populist instincts of people who would have been no more than a small and disregarded right-wing pressure group in the Tory party that I joined 21 years ago. The party has changed - and for the worse.
Nowhere, however, is the absence of strong strategic leadership more serious than on the issue of our membership of the European Union. We are now witnessing as serious a chasm in the governing party on this issue as the Conservatives experienced on the issue of the Corn Laws in the 19th century.
Unfortunately, and this has been decisive for me, it seems that the Prime Minister has come down on the side of chauvinism, reflected not only in growing Euro-scepticism from the Cabinet but in profoundly illiberal attitudes towards ethnic minorities and such unfortunate people as asylum- seekers.
Europe is our present and our future. That is why I have been dismayed that the lack of decisive leadership has threatened the advance we need to make to reach the heart of Europe. That is where Britain must be to exert its full influence, both for its own benefit and for all the nation states of the European Union, and to work together for "la culture de la paix", with international solutions to problems and conflicts worldwide.
For instance, I am involved in a campaign to promote understanding between the European and Islamic civilisations, so important on Europe's eastern borders, as we have seen in Bosnia and in our relations with Turkey.
We must draw upon the European Union's great strengths while correcting its weaknesses in order to derive the maximum benefit. We certainly need more openness, democracy and tolerance in Europe, but getting Europe right is the most important issue for our nation and every one of our citizens - for their prosperity, their jobs, their welfare and their well-being.
It is no good procrastinating, abandoning or fudging great principles and hopes in order to satisfy the Little Englanders. The debate was long ago joined and the issue decided. We have already had one referendum confirming our membership.
We should heed Ted Heath's warnings made yesterday in response to my concerns: "There is no future for Britain outside Europe. The rest of the world realises that and is astonished that we should even risk it. As therefore our future is in it, let us be positive about it and make a success out of it for ourselves and our fellow members." My own sentiments exactly. I am a Euro-pragmatist who wants to work inside the Community instead of standing sneering on the touchlines.
If Europe has been the catalyst for my decision, there have been a host of other causes which have come together in such a way that unease has turned to disenchantment and, in the end, to this tough parting of the ways.
One example is education. I have a great personal commitment to better education. I want every child to have the opportunity, as of right, to develop his or her potential and talents. Not just the sons and daughters of the rich and the middle classes, but also those in our most deprived villages, city areas and housing estates. They deserve that right as well. I want smaller classes, better teachers, a generous supply of textbooks and other literature, computer technology and modern buildings to replace those that are old and dilapidated. That means investment. But it is essential that we invest in our children, who are our nation's future, both morally and intellectually.
On the crucial issues that matter most to me - such as Europe - the Liberal Democrats have been clear and consistent. On education they have made a pledge to raise standards, even if it means higher personal taxation. The more I have found myself at odds with Conservative policies and attitudes, the more I have realised how closely the Liberal Democrats mirror my own hopes and goals.
MPs on all sides have been aware of my unhappiness. I had already resigned as a Parliamentary Private Secretary to enable me to campaign more vigorously and openly for the causes I espouse.
Europe and education are the keys to a better future, but it is now clear that Britain also needs a more fundamental regeneration of its democracy if we are to become a country of confident citizens once more. We need to spread power instead of concentrating it, and to share knowledge instead of holding it tight, thus enabling our fellow countrymen and women to extend their freedom, to get involved and to make their own decisions. I believe that the creation of freedom with responsibility represents a profound moral challenge to all of us in politics.
I am confident that as an active Liberal Democrat I can now contribute my talents to create a Britain of the 21st century which we can all learn to be proud of once again.
The writer is MP for Devon West and Torridge.Reuse content