Thanks for the replies.
I should have explained that I need for the customer to be able to leave any field on the form blank.
If somebody does submit a blank booking form I would get this string sent through to me '||||||||||||||No|||' - note that the 4th to last field (Taxed) must be set to 'Yes' or 'No' so I should never receive a completely blank order.
Recently however I have received a couple or orders like this '|||||||||||||||||'. As the Taxed field must be either 'Yes' or 'No' these orders should not be possible which proves to me there is some kind of problem occurring during the booking process.
As this has only happened once or twice I am inclined to think the problem is specific to certain computers which is why I am wondering if the solution could be in internet settings?