2 issues here:
1. The Brit is right in that the "boys in blue" will take a statement, make some vague comments about a follow up investigation & probably conclude that, since there is no actual loss & making this stick would be too much hard work, their productivity & effort would be better served by issuing a few more parking tickets! Whilst a criminal offence might have occurred (I am not an expert who specialises in criminal law) since there is no real damage that has resulted from the action just file it in the "too difficult tray" & hope nobody asks further about it.
2. Another issue is the Landlady - we know she is a Mainlander but if she resides in the PRC then there is a jurisdictional hurdle to overcome.
So, forget about launching a legal case unless u have money to burn or you can get a solicitor to agree to a "no win - no fee" (but I seem to remember that this is against the HK Law Society rules or code of practice): the only winners in this situation would be the solicitors who would still receive their fees. Just don't pay the last 2 months, return the keys to the property in a similar condition you received it (fair wear & tear excepted) and call her bluff!
When in Rome.........................