For further details see the Civil Registration sections of the England or Wales pages. For further details see the Civil Registration section of the Scotland page .
Irish records have their own system as well.
Ireland had been claimed by the English Kings since the 12th Century but was not officially joined to Great Britain until 1801. So, today, the 'United Kingdom of Great Britain and Northern Ireland' includes 'Great Britain', which in turns includes England, Scotland and Wales. The Channel Islands and the Isle of Man are 'Crown Dependencies' which are technically outside the United Kingdom and have their own local legislatures. This is course is the offical version. You will find many people referring to 'England' when they actually mean 'Britain' or the 'UK'.