There is another
thread with some useful links for finding National Grid refs and various conversion utilities.
It's unfortunate that the recording software does not allow spaces in GRs: separating eastings from northings by a space allows much more error checking. The concatenation etc., required
could be done in the software. Many GPS devices store GRs with the 100k square, eastings and northings separated by strings, and these will become more popular for directly recording data. I am now spending effort converting point records into 100m or 1k grid squares, when in principle all of this could be done when records are queried.
However, I'm all in favour of making life for recorders easier so give 'em the data in the form they want.