Why is my electric circuit breaker tripping?
Based on your confirmation that the main breaker is tripping, and your description here:


  I have switched the individual fuses that are labeled emersion switch (as we don't have one) cooker unit (this only works the clock on the gas cooker) and down stairs lights off , the power so far is staying on but if I put any off these on the whole breaker trips.


This tells me that you do not have an overload situation.  There is a short, and/or one or more faulty breakers possibly including the main breaker.

Even an experienced DIY'er with electrical knowledge would probably contact an electrician at this point.  If there is a potential problem with the main breaker then it is best to get professional help.