Found the issue. I was (as per other suggestions on this site) using body preview for the compose but this cuts off the body text. However if I use Body instead then I cant use the split expressions as its all in html
It all works well if I use Body Preview except of course its cuts off the text !

e.g. Output from the email is
......<body lang="EN-GB" link="#0563C1" vlink="#954F72" style="word-wrap:break-word"><div class="WordSection1"><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="">Membership Number: 123456768</span><br>Application Reference: xxxxxxx-56a3-427f-b18d-21b261d5db77<span style=""></span></p><h2>Employer</h2><p class="MsoNormal"><strong><span style="font-family:"Calibri",sans-serif">Exists in CRM: True</span></strong><br>Crm Id: xxxxxxx-2dae-e411-9401-005056a04b19<br>Employer Code: 123456<br>Name: a large company that is down the road from a smaller one</p><p class="MsoNormal">Address Line 1: the road<br>Address Line 2: the street<br>Address Line 3: <br>City: Romford<br>Country: United Kingdom<br>Post Code: AA01 xyz</p><h2></body>....
so the input to the compose is
....<body lang="EN-GB" link="#0563C1" vlink="#954F72" style="word-wrap:break-word"><div class="WordSection1"><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="">Membership Number: 123456768</span><br>Application Reference: xxxxxxx-56a3-427f-b18d-21b261d5db77<span style=""></span></p><h2>Employer</h2><p class="MsoNormal"><strong><span style="font-family:"Calibri",sans-serif">Exists in CRM: True</span></strong><br>Crm Id: xxxxxxx-2dae-e411-9401-005056a04b19<br>Employer Code: 123456<br>Name: a large company that is down the road from a smaller one</p><p class="MsoNormal">Address Line 1: the road<br>Address Line 2: the street<br>Address Line 3: <br>City: Romford<br>Country: United Kingdom<br>Post Code: AA01 xyz</p><h2></body>....
when I look at the input / ouput of the add a row to excel its now weird
....
"table": "Email1",
"item/Membership Number": "<html><head>\r",
"item/Application Reference": "<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\"><meta name=\"Generator\" content=\"Microsoft Word 15 (filtered medium)\"><style>\r",
"item/Exists in CRM": "@font-face\r",
"item/Crm Id": "\t{font-family:\"Cambria Math\"}\r",
"item/Employer Code": "@font-face\r",
"item/Name": "\t{font-family:Calibri}\r",
"item/Address Line 1": "p.MsoNormal, li.MsoNormal, div.MsoNormal\r",
"item/Address Line 2": "\t{margin:0cm;\r",
"item/Address Line 3": "\tfont-size:11.0pt;\r",
"item/City": "\tfont-family:\"Calibri\",sans-serif}\r",
"item/Country": "h2\r",
"item/Post Code": "\t{margin-right:0cm;\r"
which means I can no longer user
split(outputs('Compose'),variables('ParseEmail'))[0]
etc...