If its a "natural pond" no filter, UV, pump will be required.
What is the "little water feature"? you mention, and used for what?
Cleaning, now is not really a good time (too cold) but if you must, then may I suggest that daft that it sounds, a plastic dustpan and brush will work wonders.
Take any plants out and stand in a container of pond water, bail or pump out what you have left, then use the dust pan and brush to get the sludge out, put it on the side of the pond so anything you didn't see can get back into the pond.
Refill, add dechlorinator and put the plants back.
As an aisde, if a pump cable has been damaged, I would never suggest it be repaired, you can't change a submersible pump cable, (it's sealed) You can't use an ordinary connector (not suited)the pond cable repair "Kit" often leak as they are awkward to do right, a new pump is cheaper than a new life.
Good quality costs. Bear this in mind before you start.
Sorry if my reply is NOT want you want to hear, but what I have said is true.
and am I ok stripping it back comeplety and starting it again?
This depends on the condition of the pond and whether or not you have any fish. If you start over, you'll loose beneficial bacteria, but it may be worth it if the muck is deep enough. If there is a gravel bottom, consider taking the gravel out, as the biological load of the debris it traps far outweighs the surface area it provides for nitrifying bacteria.
If you have both fish and sludge, either take the fish out or clear only a small section of sludge each day. The reason for this is that the sludge will release poisonous gases when disturbed, and too much at once will kill the fish.
Well the pond didn't have any fish, it measures about 4 foot long roughly and about 1 1/2 feet wide at the widest point. I think its about 1 and 1/2 feet deep. Couldn't find the bloomin tape measure to measure lol,
Turns out there is no filter or pump in there.
The bottom was full of gravel/sludge. Is it worth putting the gravel back in once filled?
Its too small to keep any fish in, so I guess I will just have to have it as a nature pond.