Hi Doomed
I don't think there is a product available that is exactly what you are asking for.
There are sockets on a pole which are not securely lockable.
There are sockets that claim to be 'lockable' where that just means a cover clicks in place (not with a key), they can be found on a pole!
There is at least one securely lockable single socket, but not supplied on a pole!
If by "lockable" you mean with a cover physically locked with a key (eg padlock), maybe to stop vandalism or people interfering with it, the only single 13A socket with a padlock-able cover I am aware of is from this range:
available here
Find many great new & used options and get the best deals for Single Switched Socket in Lockable Box Weatherproof IP65 - Lid Closes over Plug at the best online prices at eBay! Free delivery for many products!
www.ebay.co.uk
WEATHERPROOF 1 GANG OUTDOOR SWITCHED SOCKET LOCKABLE WITH PADLOCK. COMPLETE WITH A 25MM PADLOCK AND 2 KEYS. 1 GANG SINGLE SWITCHED SOCKET OUTLET FEATURING A LOCKABLE HOUSING. A SERIES OF 6 X 20MM CABLE ENTRY KNOCK-OUT HOLES ONE TO EACH SIDE AND TWO ON THE REAR FOR VERSATILE FIXING.
www.ebay.co.uk
If you mean a lockable on/off switch with the socket, power switched by a key, there are several of those to choose from (eg MK!), but they are all twin socket form factor, and the 'lockable' cover just clicks shut, not locked with a key. A twin socket might look a bit odd on the top of a pole.
If you only need to 'lock off' the supply (eg to stop people stealing electricity!) you might be able to add a switch indoors. But that would leave a simple outdoor socket vunlerable to vandalism.
But if the above interpretation above would be acceptable, perhaps you could modify this !
Find many great new & used options and get the best deals for Waterproof Outdoor Socket On 123 Stainless Steel Post at the best online prices at eBay! Free delivery for many products!
www.ebay.co.uk
I notice there's a little bit broken off the socket cover!
or
Wide Variety Of Cables, Lamps & Lighting, Alarm Systems, Heating & Hand Dryers. Free Next Working Day Delivery On Orders Over £50. 40 Years In Industry. Same Day Dispatch. Cable Cut To Length. Better Than Trade Prices.
www.superlecdirect.com
Personally not convinced IP44 good enough for this.