It looks like a medical diversion.

Results from https://www.ExpertFlyer.comFlight Status Search:
Departing on 15/10/18
Flying BA flight 11

Flight Status Depart Location Depart Date Reliability Arrive Location Arrive Date
LHR Scheduled: 15/10/18 19:55 SIN Scheduled: 16/10/18 16:05
BA 11 En Route Term: 5 Estimated: 15/10/18 20:14 56% / 29m Term: 1 Estimated: 16/10/18 18:35
Gate: C65 Actual: 15/10/18 20:14 Gate: Actual:


Comments:
"DOBA11/15OCT
* OPERATIONAL FLIGHT INFO * BA 11 -1 MO 15OCT18
CITY INFO HOUR (LOCAL)

LHR ESTIMATED TIME OF DEPARTURE 2015
AIRCRAFT FORCED TO RETURN
ESTIMATED TIME OF ARRIVAL 1830 SIN
DEL DIV SIN DEL
COMMERCIAL PUBLICITY/PASSENGER
CONVENIENCE, VIP
ESTIMATED TIME OF ARRIVAL 0900 DEL
AIRCRAFT LANDED DEL 0855
AIRCRAFT ARRIVED AT GATE DEL 0903
NEXT INFO WILL BE AT 1000
LEFT THE GATE 1019
TOOK OFF 1050
*1A PLANNED FLIGHT INFO* BA 11 -1 MO 15OCT18
APT ARR DY DEP DY CLASS/MEAL EQP GRND EFT TTL
LHR 1955 MO FAJCDRIWETY/M 388 13:10
BHKMLVSNQOG/M
X/M
SIN 1605 TU 13:10
COMMENTS-
1.LHR SIN - MEMBER OF ONEWORLD
2.LHR SIN - DEPARTS TERMINAL 5
3.LHR SIN - ARRIVES TERMINAL 1
4.LHR SIN - 9/ NON-SMOKING
5.LHR SIN - ET/ ELECTRONIC TKT CANDIDATE
6.LHR SIN - CO2/PAX* 500.72 KG ECO, 1,001.44 KG PRE
(*):SOURCE:ICAO CARBON EMISSIONS CALCULATOR
CONFIGURATION-
388 F 14 J 97 W 55 M 303
>"