Hope that makes sense
Not particularly in the scheme of things in that are you saying there is two unrelated 1k issues or the older 1k issues is whta you are paying now ?
It makes sense that hmrc would be a pain and issue backdated tax returns , that have a habbit of doing that.
It is possible that the backdated tax returns could cause a liability - i would like to think you accountant could advise why in laymans terms - if there was no "new" income that was taxable (higher rate dividends) i would have expected that if you have previous owed tax via paye for one year then hmrc would have issued a P800 and previously collected this money - but with hmrc tax codes and P800's nothing is certain.
It just feels so unreal to be asked to pay 20 plus% on top for a dividend of less than £5k, despite having paid my normal tax for PAYE and corporation tax for that year. Does this sound right to you with this new info?
This is very unlikely to be the case presuming your total dividends are under 5k there probably is a different reason why you owe the money again your accountant should be able to explain in laymans terms whats going on. (2 situations where dividend income cause extra tax though is if your income breaches 50k ** and you have claimed child benefit or your income breaches 100k - you then lose personal allowance. Strictly speaking even then you are not paying tax on the dividend - its just causing the same extra tax nightmare that any other income would also generate in a similar manner)
I would recommend asking your accountant to explain exactly why the tax has arisen - pointing out the fact that dividend income under 5k doesnt normally trigger any specific tax charge, hopefully then you will have your answer.