does the cctv system output via scart?
if so and its just an ordinary scart lead replace it with a scart adaptor block that has an in out switch, then use a phono cable with a phono to bnc adaptor or phono to bnc cable.
you will find most cctv stuff in the industry uses bnc so there isnt much you can do.
BNC is composite so your RF out wont work im afraid, but you could use the scart out from the VCR if your cctv system has a fixed scart plug.
also VCR's are going out big style, so your local force will run out of VCR's to play back your footage, id recommend a DVR with the ability to output via a CD-R/DVD-R.
also dont be tempted to record only when incidents happen, this IS illegal, keep to 24hr recording like you are doing