Have read that putting Duct tape around a small junction box can be dangerous.

anotherquestion

Hi,

I have just replaced a few Led security lights and because the cable comes out of them, I have had to use a few small junction boxes to join up both Lights cable and the cable from the house.

There are the small junction boxes I used.

Waterproof Junction Box Connector Electric Cable Inline Wire Slim Plug IP68 | eBay UK

As I felt not totally waterproof at each end I wrapped them around with duct tape, but have now read on google this is not a good idea as could give a fire risk, and to use other kinds of tape instead.

So if you believe that info is correct what kind of waterproof tape would you advice me to use.

I do have the old wide flashing tape about, but don't want to try even to use that as not sticky enough and too hard to get on.

Thanks for any advice.

Typhoon2000

Are these low voltage lighting. If so I do not think there is any fire risk of water does get into the box.
Magic gel or similar are the best thing for waterproofing outdoor junctions boxes.

anotherquestion

Maybe Lights are low voltage but the cables themselves are fairly heavy duty looking, I actually think when I got the cabling done many years ago (old red and Black colours wires inside and a bare copper earth) it was actually wired up to a back of a plug in loft.

WIAWSNB

These connectors work well, and can be very weatherproof, but they do rely on a good seal around the cable, and in turn relies on the cable being round and of the correct size.
So, is the cable suitable?
Are the cables carrying mains voltages? Are they exposed so will get wet?
Anyhoo, I can see no fire risk from using duct tape, although I'm not sure it'll provide the best sealing either. If you really wanted an extra sealing skin, then I think amalgamating tape would do the job better. 
This is rubbery and stretchy tape, and is wrapped around whilst pulling it with enough tension to slightly stretch it. It then amalgamated, and forms a sealed skin. 
Begin wrapping around the cable for at least an inch, and continue over the connector, giving a good half-lap or so.