Thanks very much for your help - it looks as if many helpful people are
already responding to my request - Thanks to you all....

I did FINALLY manage to solve the problem as follows:

=D4-C4-TIME(0,E4*60,0)

C4 is my Start Time, D4 is my End Time, and E4 is the Lunch Time. I
tried to deduct this as hours which was ok for whole hours, so I
changed my TIME formula to multiply the Lunch by 60 (ie: 1.00 is 60
minutes, 0.50 is 30 minutes) and that worked.

Such a simple task has to be so complicated....
Thanks again everyone.