I find that even though you are 'entitled' to the 39 hr week, I feel as if I am 'clock watching' if I bring this up with management.
I am being paid 29K now, so I don't mind doing a few hours over and above the 39, without payment.
However, I found that just 2 yrs ago, when I was earning 22K and 23K, I STILL had to do 40+ hours a week. I couldn't 'be seen' to leave work at 5.30 on the dot, as it would look like I am not really serious about the work. I was an accounts assistant, working in a small office. If everyone else is doing extra hours, I feel that I have to do the same. Sometimes I think it is better to work in a large company. At least, when there are large numbers of people, EVERYONE will not be doing extra hours etc, and you are more likely to get your tea breaks, proper working hours etc.