Have we lost our working rights?

I listened to a radio program where the question of companies being unable to encourage indigenous people to work for them,
in favour of immigrant labour was discussed.
Various small businesses stated that they have to employ foreign labour because Brits are lazy, refuse to work the hours or the money being offered.
But I think think the problem is employers offering little and wanting lots.

Have we lost our employment rights?
I am a firm believer that if you are contracted 40 hours you have a right to work 40 hours. Any additional hours should be an agreement between you and the employer and paid at the correct rate. However a lot of employers like to have a contract with 36 hours and then expect you to work 40, a lot of the time unpaid.
I think this is because having a low hour contract impacts pension, redundancy and various other benefits in favour of the employer.
I don’t understand why a person contracted 40 should not have the right to work 40 without fear of bullying and also be paid a fair wage.