Unidentified Diptera

Observation - Unidentified Diptera. Description: Please can you help identify this fly; All black head, thorax and abdomen, brown legs, black haltere stalk, bright/seemingly florescent lime green or yellow ball on haltere which is very distinctive due to the lack of colour on the rest of the insect, ver

Please can you help identify this fly; All black head, thorax and abdomen, brown legs, black haltere stalk, bright/seemingly florescent lime green or yellow ball on haltere which is very distinctive due to the lack of colour on the rest of the insect, very short Y shaped antenna, about 3/4" long, mating.
I am new to the group and entomology so please forgive my lay description.