A quick question - what UK agency does the official investigation on an event such as this?
It does not fall under the AAIB definition of an "Accident" - the definition is less clear as to what is a "Serious Incident".
The AAIB have said:
In exercise of his powers the Chief Inspector of the Air Accidents Investigation Branch (AAIB) has ordered that an investigation into this serious incident be carried out, in accordance with the Civil Aviation (Investigation of Air Accidents and Incidents) Regulations 1996 and the Standards and Recommended Practices of Annex 13 of the International Civil Aviation Organisation (ICAO).
and in the 1996 Regs it says:
Subject to paragraphs (5) and (6) below, the Chief Inspector may, when he expects to draw air safety lessons from it, carry out, or cause an Inspector to carry out, an investigation into an incident, other than a serious incident, which occurs—
(a)in or over the United Kingdom; or .
(b)otherwise than in or over the United Kingdom to an aircraft registered in the United Kingdom.
which gives the AAIB powers to investigate even outside the strict definitions...