Been here last week.
Law changed couple years back, the water companies are responsible for anything from the manhole to the main, you are responsible from property to that manhole, if it's a shared drain 2 or more properties, then water companies will unblock for free,as they can't apportion blame.,
Cost 4 of us £50 each to get it jetted, then camera'd, we didn't know about the law change until, anglian water happened to turn up afterwards, and told us about the 'changed law'
So find your manhole and basically from there back is yours, it's still worth ringing your water company, and by the way 99% of blockages are caused by baby_wipes and ladies winged thingy's