First reports are often wrong. Eye witnesses are often wrong. The press is hardly ever right.
With that out of the way...
Aren't police MP5s single shot? (Assuming it was an MP5)
The witness that I saw being interviewed said the police were undercover and were armed with semi-automatic pistols.
So first reports suggest that the suspect was shot with a pistol, not an MP5. I've no idea whether the UK police MP5s are select-fire or semi-auto only. Even if they are semi-auto only, it does not take long to fire 5 shots.