Can anyone please help.  I have been advised that my fire alarm does not comply. It only has one sounder circuit. Is this correct or is there any regulations etc to say I have to have two

For a very long time BS5839-1, the standard for fire alarm systems, has required 2 sounder circuits on fire alarm systems.

Whilst a BS is not law, it is generally used as a benchmark for legal compliance and if you wish to vary from it (which you can legitimately do in some circumstances) you have to justify why the departure still provides an adequate level of safety.

With one circuit there is a risk that if something goes wrong with it then you will have no warning at all of a fire - with a second circuit at least you will get partial warning.