Thanks for the reply Spruce, it appears you can. I've just had an email from Paul and I've copied and pasted his answer below for anyone that is interested..
Run George and go to System/Invoice Addresses and create a record for the invoice account name & address.
Then select each Job you want on the invoice, go to the Job Address page and untick "Use this address on Invoice". Then click Next and select the Invoice Address you just created. All Jobs with the same Invoice Address record will appear on the same Invoice.
Please note that this is not retrospective – it only has an effect on new completions for those jobs.