Also worth mentioning in the case of Ireland the KDB, whereby you can get an effective 6.25% rate on your corporation tax for certain R&D heavy activities (software etc.). This would be advantageous I think for most smaller businesses HNers are typically involved in if they wish to operate in the EU.
And Entrepreneurs' Relief on capital gains
FYI, Ireland has not been in the UK since 1921.
FYI, if you look at OPs comments you will see they said they are in the UK.