Sewer Drain in need of clearnace

The private drain of 19/21 Copse Hill was blocked and we had a drainage company come and unblock it. There was a big blockage however the drainage company suggested the following:

The second is to get the major sewer pipe in High Cedar drive checked out.....they noticed that does not seem to be draining as quickly as it should, and are worried that if that is an additional issue then, having unblocked the storm drain, it would not just be rain water that backs up into the house (which does not bear thinking about!). With hindsight, we and other residents have experienced intermittent 'drain smell' in our apartments, and they think that could be because the main sewer is partially blocked.