The animal was identified as a Eurasian lynx and the RSPCA suggested it was probably someone's illegal pet that had either been released or escaped from captivity:
"You would not be issued with one to keep a lynx in a normal, domestic premises in north London. We believe someone was keeping this animal illegally and it has escaped. We are appealing for information from anyone who might know who the owner of this cat was."
As far as we know, the owner was never identified, but the people of Cricklewood presumably slept a little easier.