As a company that works in the NHS as I am sure may others on here do too. More and more NHS organisations are using Tradeshift. http://www.tradeshift.com. It would be good, though not a deal breaker to be able to link to this software to at send invoices and receive updates. At the moment we use the Snailmail option to link between two online systems.
Thanks for the suggestion @ALA_LTD we will definitely monitor the interest in this service. While it may not be possible to build a direct integration (there are simply too many services to consider), we do have an open API which would allow a 3rd party service to be built in order to connect the systems.