As has been said you can buy the keys for the green part for cheap or get it sorted by a locksmith.
The big thick pin is aftermarket I believe (likely Hayman Reese). You can probably get a replacement key I'd say. A good locksmith can easily open it. Alternatively, like suggested, just cut it off with a grinder (carefully!) And replacement. It looks like it's been sitting on there forever and the lock will likely be corroded and a pain in the butt day to day. They are easily replaced from the likes of SuperCheap, Repco, etc. Not expensive.
Good luck
Chris
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Chris Phillips
Offroader: 1996 Discovery 300TDI (The Green Donkey)
Missus: 2010 Discovery 4 TDV6 (Fancy thing)
Just 'cause: 1999 Discovery SE 3.9L V8 (Makes fun noises, sometimes...)
Spares: 1998 Discovery 300TDI (Only vehicle actually in the garage..........)
Run around: 2001 Nissan Pulsar ST 1.8L (Soul crusher)
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