Whether or not you are paid extra – over and above your normal hourly rate – for overtime worked will depend on your contract terms, but your average basic pay including overtime, must be at least the National Minimum Wage, whatever your written contract document says.
Where your hours and pay are governed by collective bargaining, it is likely that your employer will have negotiated enhanced hourly rates and shift premiums for overtime and anti-social hours.
Often an employer will pay staff who work anti-social hours a higher wage than those who work normal office hours. Indeed, if you are paid by the hour then you must be paid for any overtime hours that you work. This is the least that an employer can do, because working longer hours places a strain on the health of individuals and limits their ability to fully participate in the life of their family and community.
Sadly in recent years, working long days, taking work home and working part of the weekend has come to be seen by some employers as normal.
Unfortunately, there is no legal entitlement to enhanced pay for working anti-social hours, nor a formula stating how much more you should be paid for working any given hours. If you are dissatisfied with your overtime pay arrangements, consider joining together with your colleagues and (perhaps by inviting a union) negotiating salary enhancements.
Once an extra payment has been agreed, it should be recorded in writing and circulated to all those affected, as well as added to the contracts of all new starters.