Gears randomly shifting?

The closer the top jockey wheel is to the sprockets the better i.e the further upward. On some derailleurs there is adjustment for this (b screw).
The closer the top jockey wheel the more precise shifting.

I spent time this morning tweaking cables, chain and derailleurs.

Gear shifting is working perfectly! However slippage issue continues albeit now only on three smallest cassette wheels.

The chain seems okay. I checked for stiff links and tension and it appears fine.

What I can work out (as a novice) is that there appears to be a defect in the rear cassette. On close inspection the second (7) and third (6) sprocket (?) are bent or skew. For example, when select 5 you may jump to 7. When selecting 6 it jumps down to 7.

I tried to examine the teeth to determine if they are worn but cannot really tell. No individual teeth are bent or damaged.

I have attached some pics:
1) Low Gear - Positioning looks correct
2) High Gear - Positioning looks correct
3) Cassette - Doesn't really clearly show the issue, but when spinning pedals it appeared the highest gear sprockets weren't running smoothly or straight.
4) Cassette Teeth - Not really clear if any wear?

Another suggestion was to check the freehub body but not sure how I would do thsi without taking off the wheel and cassette?

Assuming it is a cassette issue - I take it I need to replace cassette and chain? Cost £50?

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The positioning in high and low is down to the stops, the indexing could be way out.
The cassette does not look particularly worn. I suspect that it may be a combination of shifter (indexing) set up and maybe sticky pawls in the free hub.
A lttle light machine oil in the freehub may fix the sticking pawls if that is one of the problems.
Setting up the indexing may then assist with correct derailleur operation.

Does the positioning look incorrect?

Would this cause the issue of the chain skipping over (not engaging) the rear cassette sprockets?

I will try some oil in the freehub to see if it resolves any sticking pawl issue.

Sounds to me like it hasn't been put back on correct.
There is a thin thin spacer that needs to be in the right place

comme ça...

After further adjusting I managed to ride my bike a few metres before the issue continued. I dropped into my local bicycle shop for diagnosis.

They pointed to the freehub needing replacing. If this doesn't fix the issue, then a new cassette and chain would be required.

They suggested instead of paying for a freehub that I replace the whole wheel for approx £50. A new chain and cassette would be around another £50.

I don't think I have much choice! Thanks for all the responses. Hopefully the new parts will resolve the issue.