The OP is assuming the drainage at the front is Combined, and it all converges into the same sewer further downstream. Sewer Maps are not always right, and again, given the age of the sewer in Victorian streets, it may sometimes be an assumed route shown if the actual route isn't known.
The only safe way to ascertain if this sewer is suitable to connect to or not would be an appropriate test, i.e. Tracing Dye. The OP shouldn't be attempting to lift covers outside of their property, particularly in the Highway, in order to conduct such a test, so the correct procedure now going forward, is to speak to the Water Company, and get their permission to connect. If the Water Company, ( Worcester I would think is under Severn Trent), have any doubts, they will perform the necessary checks before giving or refusing permission to connect.
The OP needs to be aware, if they connect without permission, and subsequently it is found that sewage is entering a surface water sewer, and traced back to their property, they will receive Legal Notice to make the correct connection at their expense. If they want to argue then they'll need deep pockets.