@engaric has mentioned that he is working on a new reader, nice work! See repo and mailing list entry and this entry

Some notes from him:

• Fix exception 'org.opengis.referencing.NoSuchAuthorityCodeException: No code "EPSG:27700" from authority "EPSG" found for object of type "EngineeringCRS".'
• Find common behaviour for OSM and OSurvey, do it via interfaces and/or abstract classes.
• Move the import process out of the core to reduce dependencies. Of course also the OSM part should move either into tools or every importer gets his separate module.
• Avoid the heavy logging like in OSITNElement or OsItnInputFile and use unit tests instead,
  which makes the import procedure also more future proof. See OSMReaderTest where we do similar stuff for OSM and just use artificial OSM XML
• For better portability (Android, JS, Objective-C) I abandoned java reflections in core and we are at java 6. So the reader 'guessing' should be done more statically e.g. similar to EncodingManager.parseEncoderString.
• Improve code formatting and class naming (OSITN vs. OsItn -> maybe OSurvey? As OS is already occupied from open source and operating system?)

(My) current instructions

#0.
git clone https://github.com/engaric/graphhopper
#1. changed the config.properties to use OSurvey: 
reader.implementation=OSITN
#2. get graphhopper.sh from official gh master and overwrite current (somehow not in-sync?)
#3. 
wget https://www.ordnancesurvey.co.uk/docs/sample-data/os-mastermap-itn-layer-sample-data.zip#sample-data-download
#4.
unzip os-mastermap-itn-layer-sample-data.zip && mv Initial/58096-SX9192-2c1.gz sample.osm.gz
#5.
./graphhopper.sh import sample.osm.gz