Conversation so far:
What did Tony Benn do in 1997?
In 1997, the Labour Party under the leadership of Tony Blair won the general election. Benn was initially somewhat sympathetic to Blair, welcoming a change of government.
What change of government happened in the UK in 1997?
[Blair] set up a new political party, New Labour“.

Question: Why did he set up a new party?
Self-contained rewrite: Why did Tony Blair set up a new political party?