I ended up being able to use the response data from Autopilot and found I was able to get the useridentifier from the json response as such:
user_name = request.form['UserIdentifier']
This has then allowed me to send direct messages via the incoming webhooks application in slack as using the above user name as the value for the channel key as follows.
payload={'text':"Ok, I'm working on it. I'll let you know when your request is ready.", "channel":user_name}
webhook_url= 'https://hooks.slack.com/services/<slack id>/<slack id>'
response = requests.post(
webhook_url, data=json.dumps(payload),
headers={'Content-Type': 'application/json'})
if response.status_code != 200:
raise ValueError(
'Request to slack returned an error %s, the response is:\n%s'
% (response.status_code, response.text)
)