I assume the connector is BNC, and the video will be composite, rather than RF as such. That's what CCTV systems tend to use, and I'm busy playing with one right now (trying to set up the recorder on my network).
If that's the case, then this kind of thing:http://cgi.ebay.co.uk/CCTV-Composite-S- ... 4aa45e1547
should do the business. I've never used one, but as you can see, it's meant for the job. You may be better finding a UK sourced one and therefore getting some support.
Bear in mind I'm not a cctv expert, just a very recent (last few days) dabbler.
CPC do one which also seems to be what you want, though you'd need a BNC to phono adaptor:http://cpc.farnell.com/cyp/cm-396a/scar ... dp/AV15920