Many thanks for your re-assuring responses. I have flown numerous times since this happened, but each time I am more anxious. I think if I hadn't got straight back onto an A/C after this, I would probably never have flown again (and about 50% of the PAX did decide not to travel again that day).
At first we did think it was a bird strike, but I think the engine surge is also completely possible - would this cause a large bang?
It would be great to hear from anyone else who works for BMI or recalls this.