Very interesting article here:
"As you can see, if you look back to the 1950s, the year of the independent backbencher, the great amateur politician, almost absolute cohesion on the backbenchers. There are two years in the 1950s, two whole years, when not a single backbench government MP defies the Whip. They have absolute 100 per cent cohesion in every single vote. Then there is a sea-change somewhere around the 1960s or early 1970s, there is a bit of debate about when and why, and for the rest of the post-war era, you see a much higher level of backbench independence, and the 2001-2005 Parliament saw the highest level of backbench rebellion in the post-war era. This idea that there has been a decline is not just wrong, it is the opposite of the truth."