Postcodes and flat numbers in British English

0 I have seen it both on the same line as the city as well as below. Which one is correct?02br
00Also, is it common all over the UK to just separate house number and flat number by a slash as in the examples below?02br
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00Thanks!02br
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00New Poster02br
0099/3 Narrow Street02br
00Historictown XX12 3ZZ02br
00United Kingdom02br
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00or02br
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00New Poster02br
00 99/3 Narrow Street02br
00 Historictown 02br
00XX12 3ZZ02br
00United Kingdom0-