extending existing shed power cable

Hi, i've just had a new shed erected approx 1 metre away from old one which will be removed.
There is power cable to old shed which is armored.
However this will not be long enough to reach new shed.
Can I get a connector which will join armored cables together safely ie underground and watertight as I don't want to run a new cable from house just for sake of an extra couple of metres.
Many thanks

http://www.cablejoints.co.uk/sub-pr...nd-joints/3m-scotchcast-resin-bk-cable-joints

These are underground cable joining kits. Would you think you will be able to utilise them?

As the shed is just moving a meter isn't there enough slack in the cable to fit an IP rated box on the outside of the shed wall. Surely in the old shed the cable must have came out of the ground, ran up a wall an into the shed and then into the installation.

Though it is pedantic as your in England this work is notifiable under Part P.

Are you also competent and practised enough to make SWA glands off, as I assume you will extend in SWA

Thanks
There is a bit of slack in cable but not enough as it runs to a junction box just above floor level in old shed then changes to standard cable inside shed.
I take from your reply that it may be more complicated than I first thought.
I just did not want to pay someone to basically put me back in the same position I was before.
I just assumed there would be a simple way to connect 2 lengths of cable underground.

To be honest with you I fully appreciate people wanting to do work themselves in this age but sometimes it is best to get someone in that will be competent to do the work.

Joining cables for underground work is quite an art, and even some less experienced electricians would struggle. Any slight dampness in the join and it will trip your RCD if one is fitted on the submain.

To be honest it would most likely be a couple of hours work for a good electrician, who will join it for you, test it for you, certify and register for you and would be cheaper than you think.