There isn't one. The Shawbury VOR is not an en-route waypoint and does not have an ICAO code (which is a different animal to its morse ID). What I understand from others is that the majority of the Mil navaids are there for the Mil and not for civilian use. They are therefore not required to tick all of the boxes required of a civilian en-route navaid. If you look in ENR 4 of the UK Civil AIP you won't find it listed and if it ain't in there you shouldn't be using it as an en-route waypoint.
If you have any queries on what is valid then the search facility of the AIS site is good.
Entering SWB as the identifier produces two entries
Identifier Country ICAO Code Type Name
SWB KZ DME SAWMILL
SWB KZ VOR SAWMILL
Entering "SHAWBURY" as the name produces no results.