"The introduction of a system of PR is very much overdue."
With PR the last General Election would not have given Labour a massive majority (or any majority at all)
The top polling parties were:
Labour 33.7%
Conservative 23.7%
Reform 14.3%
Lib Dems 12.2%
Greens 6.4%
Scots Nationalist 2.5%
No other party achieved more than 1% (although that may be because of the small number of seats they contested)

Be careful of what you wish for.

The two 'main' parties (until now) have kept power between them by virtue of not having PR. Their view may change as they start losing their influence.