Garden mains cable

Hi,
I have an outdoor garden socket already installed on an external wall.
I wish to run an extension cable from this socket to a gazebo area about 20m away.
I was planning on connecting to the existing socket using a 13A plug. Then at the gazebo end, having another outdoor socket that can be connected to.
My thoughts are that I need a 13A cable with some type of armour.
Any recommendations?
Thanks in advance

There are 13A plugs designed for weather however in the main although the socket is water resistance the plug is not, and careful consideration has to be made when something is plugged in for an extended time. Caravan and boats use these plugs and sockets which have longer pins, and no fuse, the design is not water proof but does protect against water allowing and moisture to drain out. They seem to stand being used for an extended time, and can take 2.5 mm² cable often orange colour so easy seen although colour for 230 volt is blue.

SY cable does have some armour, but the armour tends to rust so has to be replaced quite often, some has a copper earth under the steel braid, but as to steel wire armoured cable although there are some metal plugs, it is very hard to terminate in a standard 16 amp plug, and SWA is not designed to flex, hawk did a range of glands that could be used with braid or SWA but in the main we would terminate the braid with the earth core, not easy but possible, but although there are some metal plugs that will take a SWA gland having used them I would not recommend them they are really hard to use.

Remember if no fuse in plug can't fit socket direct to ring final, it needs 16A protection, fuse or MCB, RCBO. Outside must be RCD protected, and if likely the same outlet is used to charge an electric car may need a type B RCD. It really is a job for an electrician.

Is this a permanent job or temporary for an event? Are you planning on burying the cable or just draping it across the grass? What load are you planning for?

Excellent response EricMark. Much appreciated.

It's permanent running under paving slabs and soil. Going to a gazebo where I saw planning on having another ip66 socket that the cable is going to.
Plugging into the gazebo socket, there's the led lights and possibly phone chargers, speakers etc. So nothing that heavy duty

As in your other post, SWA is your best bet, properly terminated to your existing socket (glanded fixed connection, via a double pole isolator if you want) and glanded properly into the new socket (put it on a post). Your trench should be quite deep, marked with warning tape, protective layer of solids above the sand bed for the cable. Since its an addition rather than a new circuit you can DIY it but you'll need test gear to verify earth loop impedance and you need to do some sums to determine cable size. Circuit must be rcd protected from inside the house (so not an rcd socket)