Hello, I am visiting UK and connecting in Dublin but have a simple assault conviction which was about 5 years ago?

Try this page for the transit info: http://www.inis.gov.ie/en/INIS/Pages/check-irish-v...

If any border control person asks about a criminal history, it's downright foolish not to tell them. If they find out anyway, and they might, you have added lying to the mix. Not a good thing.

I am not computer-savvy enough to make links work to the pages I found, but put this in your search bar and you should get a UK government site that answers your question about admissibility after a conviction: uk gov immigration rules appendix V

When you get there, click on the little arrow on the right to expand 'immigration rules for visitors', and the scroll down to Part V 3.4

Passport Control will be at your final destination unless you are leaving the terminal en route

Unlikely to be a problem unless it is endorsed on your passport.

Answer any questions honestly

I think if you attempt to hide it, and don't mention it at all, and it comes up on a search, then you will have a problem. Just be honest, say it was 5 years ago, and you have moved on since then.

WHAT IS THE LAW in UK for your bad deed?

Border Official does not care if your state calls its whatever it calls it. What does UK consider it to be.?

You can be asked about your criminal history. YOU EXPLAIN your bad deed.

You can look up the law for your bad deed.

http://www.legislation.gov.uk/ukpga/Vict/24-25/100...

https://www.cps.gov.uk/legal-guidance/offences-aga...

They can say NO not as this time.

I've gone through customs in over 70 countries and never, ever, been asked about my criminal history. What are you talking about?

Your passport gets checked when you enter a country. So when you enter the UK it will be checked. When you go back to Dublin, it will be checked. Depending on the laws, you may get denied access to the UK due to the criminal record.