For me, a low speed issue such as this with no injuries is not a major incident.
AAIB are not required to hold the recover process up. Why? Because 1000's of people are being disrupted unnecessarily. BRS will have competent managers to capture evidence post incident, BMI will have their process for capturing pilot reports and A/C data etc. All this can be reviewed by AAIB.
All the passengers, BRS and the airline are getting caught in the middle of ridiculous over regulation here!
Edit - Looking for a job. I have worked with their counterparts the RAIB. For an incident such as this, there is nothing that won't be covered through analysis of all the above I mentioned plus interviews with the pilots, cabin crew and atc. I appreciate everyone has a role to carry out, but there will be thousands of travel plans at stake here. Get those people moving!