Reconnecting a concrete filled drain/sewer

My house is the end of a row of similar houses all with the bathroom at the front. I have a small bedroom where all the other have their bathroom and the back bedroom has been split into a smaller bedroom and bathroom. In the front garden there is evidence of a drain filled with concrete. I would like to add a cloakroom to the front of the house so would like to reconnect to the sewers. There is 10ft of front garden before the pavement then the foul sewers run under the road.
What I want to know is:-
How far is it likely the concrete has run down, is it likely to be further than the drain on my property? (I'm hoping the pavement won't need touching to access)
Who do I get in to reinstate the drainage?
Who much is it likely to cost?
Thanks