"...break your employment contract by leaving before the end of your notice period"
I had quite a different experience. I used to work for a division of a very large bank. It had been the normal thing that when anybody gave their notice that they were out of the building before the end of the day (this was around 20-25 years ago).
The bank didn't want somebody who was walking out the door in a few weeks time taking anything with them.
But then they brought in a number of Americans (from Texas I think?) to head up that division, and these guys had very different views. For example, there was one woman who was on long term sick leave and they just tried to get rid of her straight away. HR had to tell them about the actual laws here in the UK.
With myself, when I handed in my notice under the new American regime, I was informed that they would graciously "allow" me to leave immediately but that "of course" no payment in lieu would be made.
I then replied that, in that case, I was quite happy to work out my contractual month's notice (with full access to all the bank systems and data - I didn't say that part out loud of course, but that is the reason why everybody was usually given a month's pay in lieu).
After having given that response to the new American Director's PA, it was only about ten or fifteen minutes later that she came back with a note saying that I would be paid my salary in lieu of having to work my month's notice. That was quite satisfying - standing up to very overbearing Americans - I couldn't really believe that they had agreed so readily.
"...I was definitely on a four week notice. I wasn't, it was three months."
Many, many, many years ago, I used to work for Sodastream. They wanted to change all the contracts at one point and also warned about redundancies. One of the main changes that I recall they wanted was that the notice period was changed from one month to three. Quite a number of people left at this point (including myself), I remember the Finance Director asking me why I hadn't signed the new contract. I remember that I was just stalling him, as I also wanted to leave the company and didn't want to mess around with 3 months notice.
It was a good job that I did leave then as there is no longer a Sodastream office or factory in the UK.