The British Conservative Party has changed. So much so that unless it comes to terms with modern times and reality it could be out of power for many years. Indeed, when one adds to the mix the considerable constitutional changes occurring in Britain, and the real possibility of proportional representation for the general election after next, there could never be a Conservative government as such again.

All this sounds dramatic, but the process has been going on for years. Since 1975 to be exact. The party I joined in 1958 was indeed paternalistic, and a little grand, but it was also tolerant, internationalist and with a social conscience very much embodied by then in the one-nation tradition within the party.

After the untidy "emergence" of Lord Home as leader, in succession to Harold Macmillan, in 1963 the party began the process of internal natural change. Rules for the election of the leader were drawn up which must have been anathema to the Tory old guard. In 1965, they were used for the first time and Edward Heath was duly elected leader by the parliamentary party.

It is difficult to see it now but his social background was in marked contrast to that of his predecessors. The country was going through difficult times and for all his many talents Edward Heath did not possess the softness of touch, and power of communication, so necessary if the party was to survive in government. The Conservatives fell from power in February 1974, the miners' election, and early in 1975 Heath was challenged as leader and defeated by Mrs Margaret Thatcher. The change began.

It took many years to complete and for most of it the people outside, and even most Tories, were unaware of what was going on. Only now are people out there scratching their heads and asking themselves what on earth has happened to the Tory party.

Basically, the whole character of the party gradually changed. It began with Mrs Thatcher hijacking the party, largely alien to her, and locking it up, eventually in N o 10. The language of the day was, "Is he one of us?", which mirrored the division that was cultivated in party and country alike.

As general election followed general election, and aided both by war and an utterly hopeless Labour Party, in electoral terms, Mrs Thatcher was triumphantly re-elected. But what was happening to the Conservative Party underneath was the important thing.

At each election many MPs retire and progressively the old party went out and the new party came in. Out went the remaining knights of the shires and assorted gents, in came a new, more middle-class, more aggressive, more self-made Thatcherite breed.

Also by definition, this breed was more nationalistic and inward-looking than the old brigade. A Praetorian guard, called the Committee of 92, was formed by the right to protect Thatcherite values. It was so called because it was formed at 92 Cheyne Walk, Chelsea. They were opposed in internal party elections by the "Lollards", so called because they were formed in Lollards Tower, Lambeth Palace. They bear no direct link to the Lollards themselves, who were, somewhat prophetically for their political namesakes, mostly burnt at the stake.

Throughout the 1980s the old party held the majority and, difficult as some were to activate, they could use it where necessary. But the right was steadily coming into the ascendancy. Ironically, that task was not completed numerically until after the fall of Mrs Thatcher in 1990.

Before the 1992 general election there were some 120 members of the Lollards on the backbenches and more in Government. The "92" had by that time literally about 92 members. After that general election the Lollards were reduced to 65; we were unable to recruit because the left was out of fashion and we declined even further in numbers.

Before the 1997 election, the successor Macleod Group numbered 48. After that election last May, 14 members were returned, to be joined by about six coming out of government and about five new members. That is your active centre-left pro-European element in the 164-strong parliamentary party of today.

My unhappiness within the Conservative party came to a head over the last three years. I was gravely unsettled by the defection of my good friend, Alan Howarth, in September 1995 and again by that of Emma Nicholson in January 1996.

I resolved to stay on and fight the good fight within the party, which I tried to do, being actively involved in setting up the Macleod Group and the Conservative Mainstream as necessary vehicles for the task. I also could not stand the thought of letting down my Conservative supporters in the constituency as they approached what was clearly going to be a very difficult general election.

While this agonising was going on, the other dimension was the emergence of a distinct "New Labour" party under Tony Blair. The Conservative party had no response save to advocate retreat to the right and into anti-Europeanism. I stayed where I was, indeed I never moved politically. One morning I awoke to find Tony Blair camped all around me.

After the general election of May 1st, I lived in hope that the party would come to its senses and after the severe defeat elect Ken Clarke as its leader. Sadly, Michael Heseltine, who could have got elected, could not stand because of his health. But not a bit of it. There was no way we could get Ken over the top with this right-wing parliamentary party. All other elements in the party wanted him but not the parliamentary party, which had the votes. Even former centrist Ministers did not back him but went for the likely winner, William Hague.

The day before the leadership selection a pact was announced between Ken Clarke and John Redwood, who had the votes to put Ken over. That afternoon Lady Thatcher descended upon the House of Commons. The photograph of her standing with William Hague outside the St Stephen's entrance, flanked by his supporters, said it all.

She had finally won, although exactly what she has won is open to question. She subsequently entered the Tea Room and personally regaled somewhat surprised rightwing Redwoodites. Michael Portillo and Norman Lamont hit the telephone at the same time. Hague won the next day.

Where it will all end nobody knows. We now have, to my mind, a one-nation government very much of my politics. It's pragmatic, pro-European and thoroughly modern.

We have a major programme of constitutional change on the agenda, including proportional representation. We have a Liberal Democrat party on the advance.

We have a Conservative Party in a state of visible decline, increasingly cutting itself off from reality and from its own supporters, not least its financial supporters.

I obviously feel sad to have left them after so many years but that said, I now sit with New Labour with great relief. For the first time for years I have a sense of inner political happiness.

Peter Temple-Morris recently resigned from the Conservative Party after 24 years as an MP. He now sits on the New Labour benches as an Independent One-Nation Conservative. He is also co-founder of the British-Irish Inter-Parliamentary Body.