Irish mobile phones begin with 083 or 085 or 086 or 087. To dial any of those four you would dial: 00 353 and then leave out the first zero and dial the other two digits. So if you were dialling 085 9999 999 you would dial:
00 353 85 9999 999.
Just dial the UK mobile number. It does not matter that the mobile is roaming in Ireland (or anywhere else); the network will automatically locate the mobile, and the roaming mobile user will pay any applicable roaming surcharges.
Just as you would call an English landline.
To call a UK mobile from a UK landline, you always just dial the UK mobile number, exactly the same way you do when it is in the UK. The network will find the mobile automatically, and the mobile user will pay any applicable surcharges for international roaming.
You call them British. They might be preferred to be called Scottish if they come from Scotland, English is they are from England, Irish if they are from N. Ireland and Welsh if they are from Wales.
England is the country name. People from England are English. Things from England are English. The language of England is English.
+44 is the international code for England.
English or British. Britain refers to the group of countries known as England, Wales, Northern Ireland and Scotland so while either word is correct saying "English" pinpoints their origins more exactly.
Vodaphone
English
English
In English we call bread, Bread in England
00 34 and then the Spanish mobile number.