Some useful sites:
- https://technet.microsoft.com/en-us/library/ms169926(v=sql.110).aspx
- http://ssrstutorials.blogspot.co.uk/2012/10/lesson-12-using-ssrs-web-services.html
- https://dylanwooters.wordpress.com/2013/07/22/using-the-ssrs-web-service-requesting-a-report-and-rendering-it/
- http://thgurus.blogspot.co.uk/2012/10/using-ssrs-web-services-to-render.html
- http://blog.aggregatedintelligence.com/2012/11/calling-webservices-from-sqlserver.html
- https://www.codeproject.com/Articles/675762/Call-SSRS-Reports-by-using-Csharp
- https://www.teamscs.com/2015/12/consuming-a-web-service-in-a-ssrs-report/
- http://sandeep-aparajit.blogspot.co.uk/2010/02/how-to-execute-and-save-ssrs-report.html
Gubbins... 