Extending cooker cable

[F]

I need to extend cabling to a cooker, replacing the existing with longer is not an option.

Is it ok to use a junction box? Is one rated at 30 amps (Screwfix 17018) suitable?

If not, what's the best way to do this?

TIA

[John White]

Yes if the cable is up to 6mm.

If it's larger than that, use one of these