We want to put a set of deck lights round our pond and they will get power from our five way pond switch box. I was planning to cut the plug off them and wire them directly into the box the same as the pump/filter etc. The problem with this is that they all seem to have the transformer built into the plug. Would it be feasible to wire a short length of cable into the switch box, then wire an outdoor single socket to the end of that thereby allowing me to just plug in the lights with the three pin plug?
The switch box gets it’s power from an rcd protected plug so I’m pretty sure I won’t die?

yes but you’ll need to ensure that the outdoor single socket is waterproof when the transformer is plugged into it.
May be worth using a normal extension lead type single socket and housing the whole lot in a waterproof enclosure.

We’re looking at cutting up light spotlights into our decking. Got some ip68 rated lights but like you say trey have a sealed transformer box with a lead out to a standard plug. Plan is to cut the plug off and wire it into some kind of outdoor suitable joining box. Going to get power to hat from an armoured cable going into the garage where we’re going to have a small consumer unit wired in.

At the same time we may have some other lights out in the flower beds and a double outdoor socket in he BBQ shelter so I can plug in a stereo / beer fridge etc.

Beyond my experience so I think I’m going to get an electrician in to do it. I work for a bank, I know my limits!