There are a number of jurisdictions depending on the set-up where contractors can register their limited company  for VAT, for example Ireland.  When a contractor invoices via a limited company they can often encounter the issue regarding issuing invoices whilst waiting for a VAT number.  Many choose to forego invoicing until this is received which can lead to various issues including cash flow.  However, there are solutions.
Firstly you do not need to wait for the VAT number, one option would be to work out the total for the services and VAT and issue the invoice.  It is important to remember with this option the VAT amount should not be shown on a separate line.  Once the VAT number is received the invoice can be reissued and sent to the customer showing the VAT on a separate line and including the VAT number.  This enables the customer to reclaim the VAT paid, but means that the contractor does not have to wait to receive funds for work done.
Another option would be to use one the various payroll solutions that Chesterfield have in place in order to help contractors regardless of their invoicing issues.  We have several VAT registered umbrellas that would be suitable for use in the above scenario.
If you would like to discuss further registering for VAT or VAT invoicing issues or indeed any invoicing issue in general to see how Chesterfield might be able to help, please do not hesitate to contact us.