i wouldn't have thought there are any laws except they must pay the minimum national wage to all employees. Are you working in the private or public sector? the public sector have guidlines as to what to pay extra for weekends and evenings, but i dont think the private sector have to
There are laws in place re under 18s working night shift, but other than that it is a straight forward contractual matter between you and the employer.
They don't have to offer any enhancements in pay for shift work.
The only law that exists for enhanced rates of pay (shift allowance, unsociable hours etc.) is that where they exist (and existence is entirely dependent on the contract of employment) part-timers must receive the same rate as full-timers.