The past week has seemed to Emma Nicholson to be the longest of her life. She left Parliament before Christmas a Conservative, a member of the Tory party for more than two decades. She returns today as a Liberal Democrat after her political defection over the holidays.

It is not something she is bashful about or ashamed of. On the contrary, as her diary reveals, it has invigorated her. As a backbench Tory, most of her life was spent as lobby fodder, filing through the Commons to support the Government. As a Liberal Democrat, she says she has engaged in open political debate for the first time for ages. She says that the Conservative Party, in which she still has many friends, is unlike any organisation one would meet in the real world - not least because most of its members are over the age of 60. She says her brief life with the Liberal Democrats has been refreshing, in part because its staff range from the young to the old and come from a variety of backgrounds.

D-Day, Friday 29 December

As the rest of the country was preparing to say goodbye to the old year and greet the new, I was getting ready to say goodbye to the Conservatives and hello to 1996 as a Liberal Democrat. After months of doubts and days of dilemma, my D-Day had dawned, D for Democracy.

After a very late night I sleep well and wake early at my London home, half a mile from the Palace of Westminster. Big Ben is chiming six o'clock. By the time it will chime midnight, my whole political world will have been turned upside-down.

I feel remarkably calm. Excited, yes. But clear-headed, with a formal timetable in front of me. I am in control of events, anxious to avoid any premature leak of my intentions.

It's a day of earnest discussion and detailed preparation with friends, family, professional colleagues and with Paddy Ashdown and his young and professional team at Liberal Democrat headquarters. We are in countdown to zero-hour, nine o'clock, geared to the BBC news.

20.15 It is important to fax my resignation letter in good time to the Prime Minister. Off it goes and we check and gain confirmation from 10 Downing Street that it has arrived. I am astonished to learn later than John Major did not receive it at is home in Huntingdon until after the Nine O'Clock News. It must have sat on the Number 10 fax machine - a political time bomb ticking away unnoticed.

The subsequent discourtesy is that there has been no reply from him, either in criticism and anger or in sadness and acknowledgement, of 21 years' active service, till that moment, in the Conservative Party.

21.00-01.30 Adrenalin is surging, overcoming fatigue. I am besieged by requests for statements and interviews. A taxi-driver tells Paddy Ashdown without realising who I am: "Hasn't some lady joined your party? Wonderful to see a politician doing something right for once."

At ITN, Michael Heseltine begins the counter-attack, which goes on over the weekend. Not so much a roar as a whimper, concentrating on my alleged frustration at not getting a ministerial job. I am disappointed that they fail to take up the debate. Heseltine is joined by the party chairman, Brian Mawhinney, and the Defence Secretary, Michael Portillo, whom I likened in this season of pantomimes to the Three Ugly Sisters chasing the glass slipper which is my vote. But the slipper has already gone.

Flop into bed.

Saturday 30 December

Up before winter's dawn for a strategy meeting with Paddy at his parliamentary office to review progress and lay plans for a day of interviews, meetings and photo opportunities. There is no let-up. The phone rings constantly with friends, family and colleagues.

Sunday 31 December

In the early hours, in an all-too-brief period for reflection, I ponder what I have done and the reaction it has provoked. How do I feel having quit the party I have been a member of for more than two decades? Greatly relieved, I have to say, and at ease with myself, knowing deep down that it is the right thing for me. No second thoughts.

A few thoughts about the organisation I have just left - no longer the One Nation Tory party of Macmillan and Butler that I joined. It has become insensitive to the hardships of the disadvantaged and most inarticulate sections of society. It seems class-ridden, prejudiced, fratricidal and distanced in ignorance from the mass of the people. By contrast, the Liberal Democrats are vigorous, enthusiastic and pursuing policies of relevance to people. I feel I am back in the real world again.

Monday 1 January to Monday 8 January

A New Year and for me a new political life. In this first full week of my new political life, press and public reaction is still coming in an avalanche. I travel to my home in Devon hoping that the political storm will die down, but find myself still at its centre, buffeted by the media, local, national and international. Dozens of TV teams and journalists at my house. We run out of coffee, so Michael, my husband - a tower of strength throughout - goes to empty the shelves of our village shop. The telephone rings non-stop, the fax spews paper and letters pour in. Whatever the newspapers are saying, 95 per cent of the responses I get are in favour. A farmer rings to say he is joining me by going to the Lib Dems.

I am appalled by the maliceand shallowness of the Conservative party HQ's campaign. A leading Tory gets the name of my constituency wrong. Norman Tebbit alleges that I demanded curtains and furniture for my office as his volunteer vice-chairman for women at Central Office in 1984. How churlish, childish and wrong. Because I wished to encourage women candidates, including Asian and black women, he banished me to a bare back room. I bought my own furniture and fittings.

The press has turned to my private life, besieging the French farmhouse where my husband's former wife lives. She bears up magnificently and kindly calls to let us know. I read predictions that I will fade into the political wilderness, into oblivion. I doubt it. I face a new year of tremendous activity as a Liberal Democrat MPbrimming with ideas and as a human rights campaigner.

The spotlight shifts elsewhere, not least to the jackpot lottery. I take no part. I have already taken the biggest gamble of my political career.