What has the bike got in terms of security? I'm just imagining a scenario where the policeman follows the thief on his bike, but then needs to get off the bike to chase him down a narrow alley (ok, I've probably watched too many episodes of the sweeny over christmas), but he wont want to spend time fiddling around with a lock, and certainly wont want to leave such an expensive piece of kit unsecured.
I've not come many alleyways you can't get a bike down.. whether you
should is another matter, some are marked no cycling, when I was a lad in the 80s the local bobby (more about him later) would wait with his bike at the bottom of said alley and give you a telling off if he caught you cycling down it..
Why would the cop want to lose the tactical advantage of being on the e-bike, and continue the chase on foot? with todays airwave radio (often GPS equipped), even if the alley really was to narrow they could get directions to the other end of the alley and/or call for CCTV or another unit to watch the suspect should they get away... also they don't haul the suspect in by the collar like the old days, a panda car with more officers usually picks them up anyway...
A suspect on foot will tire long before the cop even on a pushbike.
The local bobby in my old area I mentioned earlier was a keen cyclist and even when in his late 40s/early 50s before retirement actually let a guy (wanted for burgling and old persons house) "run off" - kept him in sight, and then rode up to him as just as the suspect was getting out of breath and said - OK, how long do you want to keep this up for? The suspect gave himself up
BTW this cops last bike also had sirens and lights on it, never saw him chase anyone though but its happened elsewhere in TVP region apparently...