The BA flight was in volcanic ash, which as a dry substance holds static electricity much better than water droplets.
The best St. Elmo's fire I have seen was in a 737. Two huge "stag horns", one off each windshield wiper post, projecting forward through the clouds for about ten meters!
The 146 had a gap in between two bits of metal on the window on the right hand side, just the right length for sparks to jump in between. The frequency and length of the spark resulted in a "buzz" (know as P-static, P for precipitation) on the radio. It was kind of interesting to match the sparks with the buzz.
As a point, there is a theory that an aircraft experiencing P-static, or St. Elmo's fire is leaving a charged path behind it, like trailing a wire through the cloud. This means that the risk of a lightning strike, following the path to the aircraft is increased.
No photos, sorry.
