If you had data like this, with the helper col H
<b>Excel 2013 32 bit</b><table cellpadding="2.5px" rules="all" style=";background-color: rgb(255, 255, 255);border: 1px solid;border-collapse: collapse; border-color: rgb(182, 170, 166)"><colgroup><col width="25px" style="background-color: rgb(240, 224, 224)" /><col /><col /><col /><col /></colgroup><thead><tr style=" background-color: rgb(240, 224, 224);text-align: center;color: rgb(32, 17, 22)"><th></th><th>A</th><th>B</th><th>G</th><th>H</th></tr></thead><tbody><tr ><td style="color: rgb(32, 17, 22);text-align: center;">1</td><td style=";">Postcode</td><td style=";">In Use?</td><td style=";">GridRef</td><td style=";">Helper</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">2</td><td style=";">AL1 5EG</td><td style=";">Yes</td><td style=";">TL159070</td><td style="text-align: right;;">1</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">3</td><td style=";">AL10 9WX</td><td style=";">Yes</td><td style=";">TL219072</td><td style="text-align: right;;">2</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">4</td><td style=";">AL2 1UX</td><td style=";">Yes</td><td style=";">TL166039</td><td style="text-align: right;;">3</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">5</td><td style=";">AL2 2EJ</td><td style=";">Yes</td><td style=";">TL157017</td><td style="text-align: right;;">4</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">6</td><td style=";">AL2 2EX</td><td style=";">Yes</td><td style=";">TL154047</td><td style="text-align: right;;">5</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">7</td><td style=";">AL2 3XZ</td><td style=";">Yes</td><td style=";">TL129021</td><td style="text-align: right;;">6</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">8</td><td style=";">AL2 3YT</td><td style=";">Yes</td><td style=";">TL126016</td><td style="text-align: right;;">7</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">9</td><td style=";">AL3 6AD</td><td style=";">Yes</td><td style=";">TL132069</td><td style="text-align: right;;">8</td></tr></tbody></table><p style="width:10.2em;font-weight:bold;margin:0;padding:0.2em 0.6em 0.2em 0.5em;border: 1px solid rgb(182, 170, 166);border-top:none;text-align: center;background-color: rgb(240, 224, 224);color: rgb(32, 17, 22)">England postcodes</p><br /><br />
After clearing some rows you get
<b>Excel 2013 32 bit</b><table cellpadding="2.5px" rules="all" style=";background-color: rgb(255, 255, 255);border: 1px solid;border-collapse: collapse; border-color: rgb(182, 170, 166)"><colgroup><col width="25px" style="background-color: rgb(240, 224, 224)" /><col /><col /><col /><col /></colgroup><thead><tr style=" background-color: rgb(240, 224, 224);text-align: center;color: rgb(32, 17, 22)"><th></th><th>A</th><th>B</th><th>G</th><th>H</th></tr></thead><tbody><tr ><td style="color: rgb(32, 17, 22);text-align: center;">1</td><td style=";">Postcode</td><td style=";">In Use?</td><td style=";">GridRef</td><td style=";">Helper</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">2</td><td style=";">AL1 5EG</td><td style=";">Yes</td><td style=";">TL159070</td><td style="text-align: right;;">1</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">3</td><td style=";">AL10 9WX</td><td style=";">Yes</td><td style=";">TL219072</td><td style="text-align: right;;">2</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">4</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">5</td><td style=";">AL2 2EJ</td><td style=";">Yes</td><td style=";">TL157017</td><td style="text-align: right;;">4</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">6</td><td style=";">AL2 2EX</td><td style=";">Yes</td><td style=";">TL154047</td><td style="text-align: right;;">5</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">7</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">8</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">9</td><td style=";">AL3 6AD</td><td style=";">Yes</td><td style=";">TL132069</td><td style="text-align: right;;">8</td></tr></tbody></table><p style="width:10.2em;font-weight:bold;margin:0;padding:0.2em 0.6em 0.2em 0.5em;border: 1px solid rgb(182, 170, 166);border-top:none;text-align: center;background-color: rgb(240, 224, 224);color: rgb(32, 17, 22)">England postcodes</p><br /><br />
And then sort
<b>Excel 2013 32 bit</b><table cellpadding="2.5px" rules="all" style=";background-color: rgb(255, 255, 255);border: 1px solid;border-collapse: collapse; border-color: rgb(182, 170, 166)"><colgroup><col width="25px" style="background-color: rgb(240, 224, 224)" /><col /><col /><col /><col /></colgroup><thead><tr style=" background-color: rgb(240, 224, 224);text-align: center;color: rgb(32, 17, 22)"><th></th><th>A</th><th>B</th><th>G</th><th>H</th></tr></thead><tbody><tr ><td style="color: rgb(32, 17, 22);text-align: center;">1</td><td style=";">Postcode</td><td style=";">In Use?</td><td style=";">GridRef</td><td style=";">Helper</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">2</td><td style=";">AL1 5EG</td><td style=";">Yes</td><td style=";">TL159070</td><td style="text-align: right;;">1</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">3</td><td style=";">AL10 9WX</td><td style=";">Yes</td><td style=";">TL219072</td><td style="text-align: right;;">2</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">4</td><td style=";">AL2 2EJ</td><td style=";">Yes</td><td style=";">TL157017</td><td style="text-align: right;;">4</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">5</td><td style=";">AL2 2EX</td><td style=";">Yes</td><td style=";">TL154047</td><td style="text-align: right;;">5</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">6</td><td style=";">AL3 6AD</td><td style=";">Yes</td><td style=";">TL132069</td><td style="text-align: right;;">8</td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">7</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">8</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr><tr ><td style="color: rgb(32, 17, 22);text-align: center;">9</td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td><td style="text-align: right;;"></td></tr></tbody></table><p style="width:10.2em;font-weight:bold;margin:0;padding:0.2em 0.6em 0.2em 0.5em;border: 1px solid rgb(182, 170, 166);border-top:none;text-align: center;background-color: rgb(240, 224, 224);color: rgb(32, 17, 22)">England postcodes</p><br /><br />